tabbed project views

When working with different projects, it would be useful to keep each one in a separate Desktop tab - that would make it clear when loading a project that it is imported into a different dataset space. Each tab would inherit the name of the project, and loading an alignment file into a tab could also be by default interpreted as an import of a new alignment involving one or more existing sequences in the project (e.g. when adding a new alignment imported from other source involving sequences already annotated, one would want to propagate annotation onto that new alignment).