VSA - Add info icons to explain lead time / cycle time calculations

Problem

It isn't obvious how the lead time and cycle time numbers are calculated. Rather than having to hunt in the docs, users should be able to see how calculations are performed from the UI.

Proposal

• Add info bubbles with mouse-overs that tell users how the calculations are performed.

Info bubbles help users understand the stage and medium columns. Use these to explain the calculations for lead time and cycle time.

From the docs:

Lead time: median time from issue created to issue closed. 
Cycle time: median time from first commit to issue closed.'