[errai-dev] Workspaces refactoring

I started refactoring the workspaces module in order to prepare migration to a mosaic based layout. The current approach will retain the existing codebase and create a parallel, mosaic based module. Once that is done, we can still decide to to drop the legacy implementation. The basic idea behind this approach is to split the workspace business logic (aka core services, like authentication) from the look and feel. Refactoring to two separate layouts is merely proof of concept and doesn't introduce as much overhead as it sounds. But looking ahead at the changes we might incorporate in the future, I think decoupling the core services from the outermost UI elements is mandatory. This will give us all freedom of choice when the work on the user interface & user experience begins. /Heiko