The user_id is stored in the flask session. On every page load, we query
the database to get:
- the user objet (user_account table)
- the user's groups (group table) to know what the user can access

If we try to cache the user_load function, the following error is raised
when retrieving the groups:
sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <User at
0x7f51e050a940> is not bound to a Session; lazy load operation of
attribute 'grp' cannot proceed

The groups from AD are only stored to map them with CSENTRY_LDAP_GROUPS.
We don't do any query on them (get all users from one group).
As we always query them with one user, it's more efficient to store them
in the user_account table as an array than in a separate table.
This allows to easily cache the load_user function.

Note that we have to remember to add the current_user to the sqlalchemy session if
we want to modify it or access a relationship (like tokens)!

The load_user function is now cached for 30 minutes. This decreases a
lot the number of database queries.

Fix INFRA-156

Some tags (like gateway) should only be selectable by admin users.

- The query to retrieve used ICS ids was run at each iteration of the
  loop...
- Use a set to quickly test the existence of used ICS ids

Having the description field only on the Model class makes things
inconsistent.
It's nice to have a description on other attributes as well.

The generation of the QR code image is quite slow and makes the page
displaying them take a long time to load when it includes more a few.
The data never changes and can easily be cached (the repr() of the class
is used in the cache key, so if the name or id changes, the cache will
be recomputed - there is no need for a timeout).

The user_id is used to track the item creator. It's not supposed to be
updated afterwards. There is no need to track changes.

Strings are automatically converted to datetime object.
Note that datetime are stored without timezone in the database (in UTC).

text is really generic and could conflict with another variable.
body is often used for comments.

Required to create users when importing items from JIRA.

Renamed blueprint from "users" to "user" to be consistent with other
blueprints (inventory and network).

+ fix tests

This allows to easily register items via the API without giving an ICS
id.

- This will help tracking who and what was created / changed
- Move fetch_current_user_id to utils.py
- Make ItemComment inherit from CreatedMixin

Add delete and delete-orphan options to the cascade behavior:
- delete: delete from database associated cnames when deleting an
  interface
- delete-orphan: delete cname when removing it from the list of
  interface.cnames

Allow to create/delete cnames when creating/deleting interfaces

Move regex to validators.py

A gateway should be an interface like any other IP.
Use tag to identify it.

It shouldn't be possible to change the ICS id of an item.
But when registering a bunch of existing items via the API, we need to
allocate an ics_id otherwise not much can be done in the interface.
The id is required for the view and edit page.

The solution is to define some "temporary" ids that don't correspond to
any pre-printed labels.
Items with a temporary id can be assigned a real ics_id when assigning a
label.

Reserved ids start with 'ZZ' (from ZZA000 to ZZZ999)

ICS id can now be non nullable.

Description shall be filled at the host level

See http://docs.sqlalchemy.org/en/latest/core/compiler.html#utc-timestamp-function

TODO: we should be able to render HTML in the comments
Look at https://github.com/miguelgrinberg/Flask-PageDown

- Rename Host to Interface
- Create new Host table to group interfaces

There is no point displaying the LDAP groups in the profile

- All created tokens are stored in the database.
  To revoke a token, we just delete it from the database.
  Tokens not found in the database are thus considered unvalid / revoked.

- Add button to copy generated token to the clipboard

- Redesign profile page

hosttags table required for the many-to-many relationship
See http://flask-sqlalchemy.pocoo.org/2.3/models/#many-to-many-relationships

- Several IPs (hosts) can be associated to one MAC address
- Host name shall be non nullable

- refactor Network class

- network name should be unique and not nullable
- force all name fields to StringField

Don't ovveride SQLAlchemy __init__ method on db.Model classes.

See http://flask-sqlalchemy.pocoo.org/2.3/quickstart/:
SQLAlchemy adds an implicit constructor to all model classes which
accepts keyword arguments for all its columns and relationships. If you
decide to override the constructor for any reason, make sure to keep
accepting **kwargs and call the super constructor with those **kwargs to
preserve this behavior

ValidationError is catched by default by flask-admin.
It's easy to catch in the api/main.py to raise a CSEntryError.

We actually don't need to catch ValidationError as it's based on
ValueError that we already catch.

The database constraints will catch the same error
(and raise an IntegrityError).

Having some validation at the model level allows to display nicer error
messages.
We use CSEntryError exception and not ValidationError so that it can be
used both by the API and views.