assign contract to a user

[jevo]

I'm working at this feature. The manager can assign a contract to an user.
So only this user can add his time entries to this contract also the summary list can be personalized via permisson.

The assigning to a user and adding a time entry to a own contract is working now. The personal views are in progress.

[wesley-jones]

Hey jevo,
Let me know if you plan to submit a pull request and I'll help merge it in.