Replace current URL generation logic with routing classes

* deduplicates URL generating/parsing code
* gets rid of spaces in URLs
* fixes error for file names with / in them (in case they exist;
  current MediaWiki seems to disallow such names anyway)

Change-Id: I5aad43f6af1b99523c597c39befcc9db1ecab83a
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/371