Create functional tests covering the branch management feature in Simple mode

Create functional tests covering the branch management feature in simple mode. The scenarii are :

• a single user:
  • user1 creates a feature, pushes the commits, checks the history
  • user1 creates a new branch, checkout the branch
  • user1 creates a new tag, do some commits and revert to previous commits and tags
• two users:
  • user1 creates a feature and pushes it on the common branch, user2 pulls the changes
  • user2 pulls the changes
  • user1 and user2 edit the same feature, handle the conflicts