WIP: Stage selection improvements

There're two levels in commit activity to stage and unstage changes. The file level and the line level.

As the buttons to interact with changes are at the bottom of the source view area, makes sense that those buttons were aware of those two levels

• Change text of buttons "Stage/Unstage" "files/lines" if there're lines selected.
• Inverse the action if Ctrl is pressed. "Stage/Unstage" all but selected "files/lines".
• Allow to interact with lines using keyboard
  • Ctrl+Shift+Up/Down Mark current focus line.
    • Allow to select hunk lines to toggle all hunk
  • Ctrl+Space to select lines
  • Ctrl+Shift+Space to modify range selected
• Enable stage/unstage actions without Alt (where key depends on translation):
  • s stage selection
  • u unstage selection
  • d discard selection

TODO:

• There's a hang when split view is selected