Fix compile for DragonflyBSD and nightly rust

Yeah, it's 3am :)

Fixes #54 using the datetime crate's spiffy new time zone ability.

- Plain -> Style::default()

fix compile errors if git support is disabled

Finally! The benefit of having all the field-rendering code (in details.rs) separate from the value-getting code (in file.rs) is that rendering them can be tested again.

There would be an extra column, and it looked unsightly. Unsightly!

This also removes the last specific style from the details view (Plain).