appSwitcher: Add option to limit to the current workspace

appSwitcher: Add option to limit to the current workspace

Add an option to limit the appSwitcher to the current workspace. For users
that use workspaces for task separation this more convient then current
behviour. While having to add an option is unfortunate there is no way to make
both groups happy as workspaces usage differes between different users / types
of users.

https://bugzilla.gnome.org/show_bug.cgi?id=703538