Following the proposed mockups, the shortcut list must
have the ability to reset modified to non-default shortcuts
right from the listbox.
After adding the necessary API in CcKeyboardItem, adding
the user-visible elements to enable that is easy.
To make that happen, add a button that resets the
keyboard shortcut.
https://bugzilla.gnome.org/show_bug.cgi?id=769063
The collision detection code was removed in commit a0a155884e
as the cleanup was happening because the previous code was closely
tied to the user interface components.
Because that code wasn't appliable to the new listbox UI, it was
temporarily removed.
This patch re-adds this feature to work with the new code orgazination.
https://bugzilla.gnome.org/show_bug.cgi?id=769063
The current CcKeyboardPanel used to manage keyboard
editing through GtkCellRendererAccel, which was replaced
when we moved to use a GtkListBox. Because of that,
the ability to edit shortcuts is now missing.
Re-add shortcut editing capabilities through a new dialog,
which is done according to the latest mockups available.
https://bugzilla.gnome.org/show_bug.cgi?id=769063
