Added referer field to http.py, as to make it possible to use a referer. I
don't know if this was possible before, and if it was it should be removed
and the appropriate changes should be made without the http.py change.

Stock plugin output was changed so the percent change has an actual
percentage sign after it.

UrbanDictionary plugin was changed to use a referer because it didn't work
without it.
Problem with urbandict plugin fixed by replacing \r\n with a space
imdbapi.com moved to omdbapi.com, so that's fixed.
Merge pull request #57 from Atheuz/master

UrbanDictionary fixed, required me to change http.py - Also minor nitpick with stock.py