Prevent "Merge into my workspace" when there is some WIP

If there is some uncommited changes (a.k.a. WIP commit) in the user workspace (a.k.a. wip branch), he shouldn't be able to merge antoher branch into it, as for a standard local git workspace

Also we have to update the popup displayed when clicking the "Merge into my workspace" button to tell user that the merge will be pushed automatically if he's in simple or intermediate mode