Fix issue #76 : Add menu items for add source filter (IGraphBuilder::AddSourceFilter) and adding file loaded in async file reader
Drag and drop file ontop of filter supporting IFileSourceFilter or IFileSinkFilter to set source/sink file
Shift drag and drop adds async file reader
Alt drag and drop adds source filter 
Will process all dropped files in turn.


git-svn-id: http://graph-studio-next.googlecode.com/svn/trunk@156 c2f33eb2-41b2-391d-4cb4-d9d0608729ba