Editing branches in Admin Mode

As an Developer I'd like to be able to edit branches inside of JCommune so that it can be more independent from Poulpe

Acceptance Criteria

• Given Admin entered Admin Mode by clicking on the branch name a dialog should be show to edit Branch Title and Description.
• Given Admin has changed any of them, by pressing Save button the branch should immediately change.

It's not required that Poulpe immediately sees the changes.