[Branches/1.0] Added synchronization to LayerGroup
[Branches/1.0] Added synchronization to LayerGroup

git-tfs-id: [https://tfs.codeplex.com/tfs/TFS01]$/SharpMap/Branches/1.0;C107352

SharpMap/SharpMap,nhvu1988/SharpMap,SharpMap/SharpMap,nhvu1988/SharpMap