Add time entry start helper functions.

Added static helper functions to TimeEntryModel to make sure that
starting a new time entry would be done from a central place in the
shared code, instead of doing it in UI layers.
Merge tags into database correctly.

Tags coming from the backend are now merged into the local database by
taking into account the fact that the tag name should be unique.
Add generic ListModelsView.

It is possible to convery any models collection into a IModelsView now.
Add retrieving of projects available to the user.
Fix running time entry lookup in timer fragment.

TimerFragment looked for running time entries only from model store.
When the changes hadn't been commited to the model store yet, the timer
entry would get out of sync and only start showing correct things when
user minimized the activity for a second.
Make GetModel virtual.

Make the GetModel method of BaseModelsViewAdapter virutal, such that
base classes could override it with more complex behaviour.
Add time tracking start wizard.

Closes #8.