Fix #45

Fix #42

ref #42

So we can use it to search & sort
ref #42

ref #42

ref #42

So we actually test the device_id migration

ie. stop assuming that when 2 objects represent the same entity, they
will be the same instance

We now assume that entities are short lived and will be used either
readonly or from the same thread

refs #44

ref #43

fix #43

This reverts commit b56f2cb2.
This makes all tests fail in a clean environment

If the main connection (ie. the medialibrary instance) were to be
closed, but a thread had acquired a connection at some point, the
connection wouldn't have been closed until the thread exited

This was preventing the database to be flushed between each tests on
windows

Fix #39

refs #39

Fix #37

Which stores whether the thumbnail was generated by the medialibrary
itself or not.

Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>