Address feedback about the overview board

We have had the following feedback about the board:

### About CAGR

* The CAGR numbers were expected to be a comparison from the numbers in one month to the same month from a year before
* I believe the CAGR / CMGR calculations are correct, but they are not what was expected
* We can also deliver a "this month last year" report and see which we like the best
* More descriptions on reports might help with this

> I've added a this month last year comparison and added more descriptions on reports explaining them. I think we might want to revisit the CAGR / CMGR calculation as it's based on whole years, so I suspect it will go massively negative in January. Should this be based on a trailing two year period?

### Annotating users in H looks too small compared with active LMS users (solved?)

* The number of "active" LMS users this month, and the number of "annotating" H users looks out of whack
* We do count activity in LMS and annotating in H differently - This could be correct?
* We could be counting different months?
* It could just be very bugged?

> So far this just looks correct - You can't directly compare annotating H users with and active LMS users

### Incorrect last month (solved?)

* The "last whole active month" doesn't look quite right. It should have changed to November here but doesn't seem to have
* Could this be the cause of some of the discrepancies above?

> Our date ranges weren't quite correct. I've set these to both the "last two months", but I have a feeling Metabase might mess this up throughout the month. We'll need to keep an eye and see what happens.