[Twisted-Python] making appveyor a required status

[Glyph Lefkowitz]

Just a bit of Github housekeeping: Appveyor has looked pretty stable (more than our other Windows builds, even).  I'm thinking about making it a required status for merging.  But I'm curious what other folks have seen on PRs I might not have looked at; is it pretty reliable at this point?

Also: I am thinking of turning off push statuses for Travis (for every branch but trunk), and just making it PR statuses.  Is anyone using the push status, or is it just making builds take twice as long?

-glyph