activeCollab service refactor

In this PR:

- silently dropping support for activeCollab3 (I doubt anyone was using it), and specifying activeCollab 4.x is required
- use the new `my-tasks` API callback to get all tasks in one API call instead of dozens
- add milestones as tags
- set UDAs to appropriate data types (numeric, string, date)
- set priority based on activeCollab value

I'm having trouble fixing the tests for date and tags. Once that gets fixed this is ready to merge.