Added pomf.se WebM and MP4 support

Added support for WebM and MP4 video formats for the website http://pomf.se

Request from Reddit: http://redd.it/293ee6
with a user base of over 2 million, this is pretty much a necessity, to be honest.

when a video opens and fails to play, we're going to get loads of posts to /r/Enhancement / /r/RESIssues calling it a bug from users who don't understand what video format(s) their browser supports (and understandably so, they just want stuff to work)...

I think we need feature detection in order to merge any PR relating to webm/mp4

also, am I incorrect that all links to pomf.se seem to directly link a mp4 or webm video? In this case, we don't really need a sitemodule but would probably rather do what we already do generically for links ending in jpg etc... there doesn't seem to be any site specific work being done here (e.g. translating a URL to a different one, or querying API data) unless I'm skimming too fast here?