Allow project branch data to be exported to CSV

Description

In our relative small project (3-8 developers) we noticed that we had over 100 unmerged features/branches, sitting there waiting to be merged. Some feature were over 1 years old, making it almost impossible to merge due to code base changed so much over the course.

This is probably due to poor management. What we did was manually put these branches down on a spreadsheet with links to the corresponding redmine tracking issue.

Proposal

Improve the "branches" page to make it easier to work with.

• An export functionality to CSV/XLSX of all the branches. The export should at least contain the link to the branch and a name.
• A more fine grained filtering of branches, such as unmerged/merged branches and improving the "Filter by branch name" to include reg-ex or wildcards at least.