Split TTR/Activity reports into summary and full

[chadwhitacre]

We post weekly Slack reports for GitHub TTR and Activity. In order to make them more effective it would be great to have only a summary in the main channel message, with more detail in a thread.

For TTR (post-#682) I would propose just the high volume section for the main thread (or low volume if there are no high volume teams that week):

┌────────────────────────────────────────────────┐
| Team                          │ % on Time      |
├────────────────────────────────────────────────┤
| ospo                          | 100 (22/22)    |
| mobile-sdks                   |  85 (11/13)    |
| web-frontend-sdks             |  81 (26/32)    |
| web-backend-sdks              |  68 (15/22)    |
└────────────────────────────────────────────────┘

For Activity we could do top 5 discussions/employees in the summary, and top 20 in the thread—or maybe top 3 and 10?