Set Time-Tracking-Mode per User

[xstable]

Describe the problem

It would be awesome to have the ability to set the timetracker-mode per user (and not just for the whole Kimai-Installation).

Describe the solution you'd like

Best solution would be to have one System-Wide Setting for it (as it is now), then an additional "overwriting" per User.

Means:

1. User overwrite System-Settings,

[kevinpapst]

Thanks. Removed project as this is out of scope