- catch IntegrityError on patch
- disable autoflush (IntegrityError was raised before commit due to
autoflush)

Pass ?qrcode=true as query string

Can use:

  -  /api/items?serial_number=123456
  -  /api/items?location_id=1

- add more tests
- patching an item update children location and status
- setting the parent on an item updates the location and status with the
  parent ones

Put under the functional directory all tests that require
access to the database. There is a "session" fixture in that
directory that is automatically invoked for each tests. It rollbacks
any transaction after the test to leave the database clean.

Other tests should go under the unit directory.

Inspired from:
- https://stackoverflow.com/a/38626139
- http://alexmic.net/flask-sqlalchemy-pytest/