Reorganized aliases in the git plugin.

This reorganizes completely the way each alias is defined in
the Git plugin. They now follow a common logic:

- they are organize in group with the same prefix, some may overlap
  (like gc for git commit and gco for git check-out) but there is
  no more collision (gp for git push and gpr for git pull --rebase)
- they are much easier to learn since they are no more in a single list
- more documented!
- they are logicaly liked to each other, they do not hide the
  underlying git command so you can easily remember them when you
  have to work on a machine without these magic aliases.
- I use them daily in my git workflow (pull/rebase, dev, rebase, push, ...)
  on both my android tasks and github projects.

Signed-off-by: Gaetan Semet gaetan@xeberon.net