Repository mapping should force default if one-to-one match found

Currently if a project is Crucible is set to have a default repository mapped, it still asks the user to specify which project they wish to create the review under. This is to accommodate the scenario in which multiple projects are mapped to the same repository.

If there is only one Crucible project mapped to a given repository, when creating a review out of that repository, rather than asking the user to confirm the project, it should force the default mapping.

The user could then override this in the review properties when assigning reviewers/moderators if required. Although being able to prevent this would be good too, probably as a project/repository mapping option "Allow users to chose another project instead of this default".