gitconfig: diff and reset aliases

* Separates diff(tool) aliases better.

* Adds unstage aliases.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
vimrc: indentation tweaks

* Disables option that auto-indented git commit message bodies erroneously.

* Groups indentation and syntax highlighting options.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>