Removed duplicate code in task lists views (now using a single class
with constructor parameters). Added specific display for assigned tasks
that have missing dependencies.
A description field has been added to items in the database, form fields
have been added to both item creation and modification. Removed some
French text that was still around.
This initial import is a heavily modified version of the code I had
here, as Arse was modified for other purposes in the meantime and the
application no longer worked with it.
In addition:
* I did not import the user management part yet,
* task dependencies are supported in-base, but there is no interface
for that yet.
