emacs: use rgrep instead of ack-and-a-half.

I didn't previously know about rgrep, and thought the grep-find
interface was clumsy, which was why I tried different tools like
ack. But the rgrep interface is better than ack-and-a-half's (and is
identical to vc-git-grep's) so it should be used instead as the fallback
when searching for files not in git repos.

Bind rgrep to "C-c G". vc-git-grep is bound to "C-c g".
emacs: new windmove keybindings

C-c j for left
C-c k for down
C-c l for up
C-c ; for right

need to stop moving my hands to the arrow keys as much
emacs: change magit keybindings

Remove "C-c l" for log and "C-c b" for branch manager. They open the
buffer in the wrong window, unlike status which I've configured to use
the current window. Instead go to the status window, then to log or
branch manager if necessary (but usually I can do what I want from the
status buffer).

This means magit-blame-mode can be moved to "C-c b" instead of "C-c B",
and "C-c l" is now available.