Add slack activity to release report.

[brianjp93]

• fixes #1367

[brianjp93]

[brianjp93]

I'll leave it up to @rbbeeston to present the data however you'd like. I just made it mirror what was being shown for the mailinglist data for now

[vinniefalco]

I think we should show activity by channel, and only counting channels starting with "boost". And sorted by activity

[brianjp93]

Example with 2 channels on a page, I only have the boost-website channel so I just duplicated it for this example.