move bindings from magit-status-mode-map to magit-mode-map

Move some key bindings that do *not* depend on the existence certain
items (which might not exist in non-status buffers) from
`magit-status-mode-map' to `magit-mode-map'.
magit-{,un}stage-all: require confirmation
magit-mode-map: cleanup

Move a line in `magit-mode-map's definition.  Not the key binding; the
line setting (the same) binding.
magit-reflog-mode-map: don't duplicate binding from parent keymap
add magit-key-mode-popup-dispatch

Note that some "bindings" conflict with those in
`magit-mode-map': "v" `magit-revert-item' and in
`magit-status-mode-map': "s" `magit-stage-item'.

We have used up most alphabetic keys, so that is
hard to avoid.
Merge branch 'dispatch-v2'

Conflicts:
	magit.el