Make Scarf usage reporting in major+minor versions and counters in buckets

[jscheffl]

As I was (together with @kaxil ) taking a look to the Scarf reports I saw some minor improvements we can have for the collected metrics:

1. We are not actually interested in the (exact) Python version but Major.Minor is sufficient. Too preceise metrics are not getting a good report
2. Same for DB Version. Major+Minor is sufficient
3. Count of DAGs, Timetables and Plugins is also too precise, made a set of buckets as the Rough number is what we want to know

I think we are atm cutting the 2.10 release but I hope somehow we get it it, if not then 2.10.2 :-D

[jedcunningham]

I'm curious why we didn't do buckets for the other counts too - flask blueprints and appbuilder views/menu items? Just that we don't think we will have that wide of a range to begin with?

I think the current buckets make sense for DAGs, but not so much for plugins and timetables. We loose basically all granularity.

[kaxil]

Fair point @jedcunningham - feel free to PR tour change