Allow more date formats

This is a pretty big PR which enables 3 more modes (so now there are 5) you can enable via the Git settings:
0. Formatted using local date format (_already existed_)
1. Relative time (_already existed_)
2. Intelligent mode (relative/formatted) (_you'd call that the Facebook mode_)
3. Formatted using your own format (_another input will show up where you can enter the format_)
4. Original Git date (_not much work there :P_)

A german translation will come later.