SystemWindows searchable in index

When a query is performed, any open SystemWindows (currently running programs and Windows Explorer Windows) will appear in the results to be acted upon like the Current Window Proxy.

This is the first planned implementation of the RealTime itemssource. Because interop with the Win32API through interop is expensive, the itemssource will contain a "SystemWindowManager" which will run on a separate thread to keep a frequently updated cache of running SystemWidndows. This way they will be immediately ready to be handed over when they are asked for by MightyBox. Most of this code is already written and will just have to be transferred over from the DOMercury code repository.