Don't remove empty workspaces when in workspace view

Automatically removing empty workspaces results in a few bad things:
* you can't freely rearrage apps how you want because as soon as you move only app from a workspace and switch to another it gets deleted
* you can't "swap" apps for their workspaces: say I want to move app A to workspace B, and app B to workspace A, this isn't possible since as soon as you switch to workspace B, workspace A is deleted
* it causes unnecessary animation shift in the view itself

Empty workspaces should be cleaned up when the user actually quits the workspace view.