Merge pull request #183 from nierob/master

Small improvements
Expose static roles in EnginioModel.

It make sense to use as much as possible of static roles in C++.
Fix tst_EnginioModel::enginio_property autotest

qWarning stream operator doesn't work with QTest::ignoreMessage. Ah how
many times I can fall into that trap.
Do not call model reset twice on setEnginio.

enginioChanged signal is already connected to execute function, we do
not want to call reset twice.
Introduce AttachedData concept in EnginioModelPrivate

Quite often we need to add internal data to _data. We can not do it
directly because such data would be visible to an user. AttachedData
is not meant to be used for all items in the model, but only for items
in a special state, for example during an update. Access to the state is
through an object id which is constant, so more reliable then row
number. That feature should fix _synced flag and some race conditions:

 - Appending two, independent items.
 - Appending an item and removing an other one