[hostingbulk] Add new extractor

Hi,
this adds support for [HostingBulk](http://hostingbulk.com/) and addresses #3703.

Things to note:
* There is more useful information on the download site (for example, audio and video codec and bitrate, upload date, uploader name), but it resides in a section which is commented out, so, I'm not sure if it's there to stay. Also, I've found that video/audio quality information is inconsistent between different videos, so it's a bit tricky to write a proper regular expression. 
* The download URL can be constructed from the obfuscated javascript, without the additional POST request. But, as I'm not sure if the javascript structure doesn't change between (some) videos (or if it will not change in the future), I didn't use it. If you think that it's OK to use it, please comment, and I will change it, or, off course, feel free to change it yourself :wink: 

Other suggestions and improvements are welcome.