Branch checks on freshly cloned exercises

[rcraggs]

When running GitRuler on freshly cloned exercises it does not 'see' the remote branches unless they are explicitly checked out by the user first. Possible solutions;

• An additional setup step that is run on the first time that checks out a named list of branches (similar to setup files)
• For the actual checks/rules, a branch is fetched before the check takes place
• The checks work on remote branches