allow to see each scm provider as a view in scm view container

Currently the scm view container shows a state of only one scm provider. It is not practical while working on multiple repos, for instance via git submodules, i.e. one has to always switch between scm providers via the status bar to check the state. It would be better to be able to get an overview of all scm providers. Selecting one or another scm provider in the view container then should automatically update other views including the status bar entry, i.e. it should become active.