Add --branches/--remotes support to logging

This PR introduces `=b`/`=R` keybinds to specify `--branches`/`--remotes` git log options.

To make it work, I removed `shell-quote-argument` from `magit-key-mode-command`.  I am not 100% sure this is safe, but at least there are some cases this does the wrong thing.  For example, `l =g .* RET` matches only commits which contain `*` in its message, which is wrong.