Freeze break request, Keyboard Settings

[Bastien Nocera <hadess hadess net>]

Hey,

The redesigned Keyboard Settings landed shortly before GUADEC, and I
had hoped that there would be less to fix up after the initial big
commit so that we would be entering the code freeze in a good state.

The following bug has a number of patches:
https://bugzilla.gnome.org/show_bug.cgi?id=769314

That make it match the designs, and fixes a number of bugs. There will
probably be a small follow-up patch, as some keybindings can't be
captured right now.

If somebody wants to test this patch set, the (reverse, as per git log)
order of the patches is:
keyboard: Don't apply "Backspace" straight away
keyboard: Add helper to detect empty keybindings
keyboard: Fix grabs not working when showing the dialog
keyboard: Don't regrab the keyboard after an event
keyboard: Don't rely on events to grab keyboard
keyboard: Don't grab the mouse pointer
keyboard: Remove unused variable
shortcut-editor: show custom page while waiting for input
shortcut-editor: move widgets into a stack
shortcut-editor: update reset button position and style
shortcut-editor: use a different page to edit custom shortcuts
keyboard: add enter-new-shortcut asset
shortcuts: remove bottom label
shortcut-editor: hide editing dialog on Escape
shortcut-editor: use states to handle headerbar mode
shortcut-editor: add 'Set' button
shortcut-editor: update header title message
keyboard: use a better icon to represent "Reset Shortcut"
keyboard: make Add button insensitive after editing
keyboard: change standard shortcut top label

Cheers