Make all compound actors layoutable

[gmc-holle]

Make all compound actors - actors with have children like XfdashoardLiveWindow with its label and close butter - layoutable. So themers can also change the basic visual appearance which cannot be changed via CSS like layout and so on.

[gmc-holle]

This affects the following actors:

• XfdashboardButton (text and icon)
• XfdashboardLiveWindow (window title label and close button)
• XfdashboardLiveWorkspace (workspace name label)
• XfdashboardSearchResultContainer (title label with clickable icon button, "more results ..." and "all results ..." button)
• XfdashboardTextBox (primary and secondary icon buttons and ClutterText text-box)