FR #988 - Allow ThankYou generator to know about all translations

I rewrote the generator to be reusable for additional years...

This now picks up ALL translations available from MediaWiki; I'm
not sure how it handles local variants yet (e.g. if we can do es-ES
and es-MX.)

We are now using the Html2Text contrib code from
https://github.com/mtibben/html2text
commit adbf1a036ec27300450f351f78ff634c79b36df8

Change-Id: Id490ca87fd0caa2b5a646c299d7395624372dd02
New thank you message

Change-Id: Ic523b7e34fc7be54ba2bb4c8394bdaab9a857c9d