Expand compare date

This merge request has two pieces:

1. Expand the Activity Date Comparison to be able to compare to date fields on the Contact. A few fields were changed to make the UI a bit more intuitive. It should be backwards compatible, but I did not have very many of the rules to test with.
2. Add support for Participants and Events in this Condition. I considered adding a separate rule for these, but the code would have been almost identical.

I am going to be using this condition in a live setting, but additional testing would be helpful.