Add broker for Weblate (BB-7735)

Hello,

A short while back I wrote a broker for Weblate. I didn't want to submit
it before the Bitbucket hook was actually available on Weblate too. But
it is now!

So: https://bitbucket.org/Freso/weblate-bitbucket-broker

If you need to make any changes to it, I'd appreciate it if you submit
pull requests I can pull in. Also, feel free to point people to the
project/repository for an example of a broker that's out in the open.

–
Namasté,
Frederik "Freso" S. Olesen http://freso.dk/