Rewrite of KWin's Screen Edge Handling

This rewrite is mostly motivated by the need to handle multi screen
setups correctly. That is have edges per screen and not for the combined
geometry. Also porting from XLib to XCB has been a motivation for the
rewrite.

The design of the new ScreenEdge handling is described in the
documentation of ScreenEdges in screenedge.h.

In addition the following changes have been performed:
* move configuration from Options to ScreenEdge
* add screen edge information to Workspace::supportInformation (obviously
replaces what had been read from Options)
* have Workspace hold a pointer to ScreenEdges instead of an object
* forward declaration of ScreenEdges in workspaces.h, this explains the
seemingly unrelated changes of just another include in some files


FIXED-IN: 4.11