workspacesView: Make each WorkspacesView own its set of workspaces

workspacesView: Make each WorkspacesView own its set of workspaces

Right now, the workspace update code is complex and spread across parts:
WorkspacesView takes a set of workspaces and looks like it owns them, but
WorkspacesDisplay is actually in charge of setting them up and creating
new ones for each WorkspacesView.

Change initialization and handling to move all of the creation/destruction
responsibilities to WorkspacesView.

We pass in monitorIndex into each WorkspacesView, which is a lie in the
workspacesOnlyOnPrimary case, as the primary WorkspacesView currently has
the responsibility of handling the extra workspaces on all the other
monitors. The commit will clean this up and punt the responsibility back
to WorkspacesDisplay.