It's not a typical singleton as the ctor is not taking a Workspace* and
needs addtional data to be passed to NETRootInfo.
All the initialization code is moved to RootInfo::create() and the tear-
down code is moved to RootInfo::destroyed(). This includes the support
window which used to be a member of Workspace. It's only needed by
RootInfo, so there is no need to have the ownership inside Workspace.
Instead of using a QWidget we just create a normal window through xcb.
It gets destroyed again in the tear-down code after the RootInfo got
destroyed.
REVIEW: 110238
Main motivation for this change is that it's unhandy to have the class
definition in workspace.h and client.h while the implementation is in
events.cpp although nothing in events.cpp uses it directly.
By getting it out of workspace.h we get the header a little bit smaller
which should improve compile time given that it's included almost
everywhere.
In events.cpp the enum usage is changed to NETWinInfo as that's the class
where they are defined.
RootInfo does no longer hold a workspace pointer. Where it's needed it
uses the singleton accessor of Workspace.
REVIEW: 110199
