emacs: Move ?, q, s, m, =, and G to the common keymap

The only user-visible effect of this should be that "G" now works in
show mode (previously it was unbound for no apparent reason).

This shared keymap gives us one place to put global commands, which
both forces us to think about what commands should be global, and
ensures their bindings can't diverge (like the missing "G" in show).