Pause dynamic workspace management while workspaceSwitcherPopup
is shown so as to eliminate infinite creation and destruction of
workspaces, thus preventing stuttering while trying to move a
window to last workspace.
Add _isWorkspacePrepended flag to make sure only a single workspace
is prepended at a time thus preventing the possibility of prepending
infinite workspaces while dynamic workspace management is on pause.
Prepend a new workspace by creating a new workspace instead of only
shifting the windows to next workspace so that the workspaceSwitcherPopup
may appear in sync with what's happening behind the scene and display
correct number of workspaces.
https://bugzilla.gnome.org/show_bug.cgi?id=712778
aeb971c33a