Add half-life event member updates

[maurolacy]

Closes #203.

Opted for straightforward changes for the fix, instead of a full refactoring. Member.points is unsigned, and adding more complexity to update_members doesn't look like a good idea. In fact, perhaps it would be better to break down update_members into add_members and remove_members (as suggested in the past), and then add a new halve_members in parallel.

TODO:

• Unit tests. (done)
• Migration handler update member msgs fixing code (done).

[maurolacy]

This bug shows the limits of unit testing, by the way. Everything is properly unit tested, and still this is wrong, and fails in an integrated environment.