Better milestone navigation in Backlog

[PeteGoo]

When you have lots of milestones in the backlog with lots of tickets it becomes hard to navigate through them.

1. Sync Milestone detail panel with Backlog panel scroll position. i.e. when I cycle through milestones in the detail panel the backlog, if grouped by milestone, should auto-scroll to the start of the selected milestone
2. Clicking on a Milestone grouping header in the Backlog section should open the detail panel for that milestone.