Show Firefox merge dates inline with comments

[bgirard]

When working on a bug you'll often see something like:

Sample User 1 week ago Comment 14 I tested this on aurora

Other User 1 day Comment 15 Fixed on central + aurora

I'd love if we could insert Firefox merge date to make it obvious that the bug got merged to a release and that beta now needs to be merged:

Sample User 1 week ago Comment 14 I tested this on aurora

Approximate time of merge: central: Was 20, now 21 aurora: Was 19, now 20 beta: Was 18, now 19 release: Was 17, now 18

Other User 1 day Comment 15 Fixed on central + aurora