Move shortcut settings into "Configure Krita" menu
Summary:
This is desirable because it lessens the confusion of having "Canvas Input Settings" and "Shortcut Settings." Users can see at a glance that both pages are available. I think it looks nicer, too.
Class renaming and documentation updates can be done in a separate patch.
Reviewers: Krita:_next, dkazakov
Reviewed By: Krita:_next, dkazakov
Subscribers: dkazakov
Differential Revision: https://phabricator.kde.org/D1121