branch: reorganize verbose options

`git branch -v` before:

  fc/branch/nice-verbose 4761939 [master] branch: reorganize verbose options

`git branch -v` after:

  fc/branch/nice-verbose 4761939 [ahead 1] branch: reorganize verbose options

Showing the upstream tracking branch is more important than how many commits
are ahead/behind, after all you need to know ahead/behind compared to _what_.
So now `git branch -v` shows the upstream, but not the tracking info, and
`git branch -vv` shows all information (unchanged).

An additional benefit is that `git branch -v` is now much faster:

Before:

 git branch -v  0.01s user 0.01s system 90% cpu 0.014 total

After:

 git branch -v  1.67s user 0.03s system 99% cpu 1.698 total

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>