+ fix tests

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

Split API in different blueprints like for the web UI:
- users (login)
- inventory
- network

Use version in API url (api/v1) to make future changes easier without
breaking backward compatibility

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

- Only admin should be able to create networks
- Deleting an interface should require at least create group (should
  that be restricted to admin?)

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

Used to validate a list of strings against a regular expresssion.

Create macro to add delete button with modal dialog
to cancel or confirm deletion.

To check if the unique object is the one being edited, we need to store
the object used to create the form in the form (_obj).
This is inspired from flask-admin.

Use inheritance to avoid duplication

cellspacing="0" : to avoid double lines in the header
width="100%" : to have extra fields (search, paging...) aligned properly with
the table

When registering a new host, only admin users shall be able to select
networks marked as "admin_only"

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.

Allow to customize the default selected values:
- the default network prefix can be defined in the configuration (default to 24)
- the default first and last IP chosen can probably be improved
  it defaults to hosts[9] and hosts[-5] if the list has more than 15
  elements or the first and last otherwise

Note that when using a small prefix (< 19), the number of possilbe IPs is quite
large and updating the first and last IP select field takes some time...

Scroll up to ensure the from input is not hidden below the navbar.

See https://github.com/twbs/bootstrap/issues/1768

Rendering done client side using Showdown: http://showdownjs.com
Live preview is shown below the form.
Only raw text is saved in the database (no HTML).

Note that no XSS filtering is done!
See https://github.com/showdownjs/showdown/wiki/Markdown's-XSS-Vulnerability-(and-how-to-mitigate-it)

Markdown to HTML converter in Javascript

Use endpoint argument to avoid collision with flask-admin Network

If a selectfield is disabled, None is returned (not a string).
To pass wtforms validation, that value shall be part of the choices.

We use None as the value for SelectField that are optional (instead of
'').
We were previously converting '' to None when creating a model.
We now use the coerce function to let the form convert 'None' to None.

- disable item field for virtual hosts
- pre-fill interface name with hostname

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

- Main blueprint used to declare custom views for all blueprints.
(keep inventory blueprint cleaner)
- Add url_prefix to each blueprint

See http://getbootstrap.com/docs/4.0/components/input-group/#button-addons