Gestures: ListBox to -> ItemsContro.

git-tfs-id: [https://tfs.codeplex.com:443/tfs/TFS15]$/Atomix;C41232
MVVM: Add support for multiple selected files.

git-tfs-id: [https://tfs.codeplex.com:443/tfs/TFS15]$/Atomix;C41233