Better support for keyboard usage

[JetpackDuba]

Add options to make easier to execute actions with keybindings.

It's mostly relevant when pulling, pushing, fetching, stashing, etc.

[Philipp91]

How about keyboard support for:

• navigating through lists (e.g. the commits or the list or staged/unstaged files) with KeyUp/KeyDown as well as J/K (same shortcuts as GMail uses)
• staging/unstaging the selected file with Return/Enter key
• switching between repositories with Ctrl+[Shift+]Tab
• focusing the commit message field with / (similar to GMail etc. focusing the Search box like that)

[adam-ce]

git cola uses control + p to push, control + shift + p to pull and control + s to stage the current file.

I'm currently still using git cola to commit changes. one of the main reasons is the better commit control. i often only want to stage part of my changes. so i select and press s.

[sabreu-teknorix]

For more flexibility, Gitnuro can expose functions like push, pull, stash, etc, and the user/developer can map them to key biddings