Cycle between windows of the same desktop on switch

Summary:
When switching virtual desktops using shortcuts, the behavior is to
switch to a virtual desktop in the opposite direction if the current
one is on the edges of the layout. For example, in a one row layout with
4 virtual desktops, "Switch One Desktop to the Left" while in virtual
desktop # 1 will send the user to virtual desktop # 4. Likewise, in a 3
rows layout with 9 virtual desktops, "Switch One Desktop Down" while in
virtual desktop # 8 will lead the user to desktop # 2.

This patch uses the same behavior whilst changing windows using
"Switch to Window Above|Below|to the Right|to the Left".
For example, in a 3 display set-up (my set-up), the user would go from an
application in the rightmost position to an application in the leftmost
position using just one key combination: "Switch to Window to the Right".
Currently, the shortcuts are no-op in these cases (ie, trying "Switch to
Window to the Left" from the leftmost window has no outcome, which is
mostly accurate with the shortcut semantics but totally useless in behavior).

Reviewers: #vdg, #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: luebking, subdiff, colomar, graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D3602