Breakdown branches by default, active and stale

It'd be nice when viewing the branches page, they were grouped by default, active and stale. Example: https://github.com/bp74/StageXL/branches

Current view looks like:

Design

Stale branches are considered stale after 3 months!

[Stretch]: Take it one step further and include a tab for the locked branches (which also makes the "locked branches help text" only needed within that tab.

Note: tab title should state "protected", not "locked"