Add up/down/left/right shortcuts for MoveTool

Summary:
Only able to move selection one pixel at a time, for now.

Integrates with current stroke framework, so if a move is currently in progress, will move a selection or group. Otherwise it defaults to moving current layer or selection.

Reviewers: rempt, Krita:_next

Reviewed By: rempt, Krita:_next

Subscribers: rempt

Maniphest Tasks: T117

Differential Revision: https://phabricator.kde.org/D738