[Feature] add support for static/seo URLs

This PRs replaces the ugly browse.php, details.php and search.php with nice seo URLs. It's done using a new dispatcher.php class which is parsing the URL and forwarding the request to the AddonController. This logic can be extended in future by adding new rules to the dispatcher and custom controllers for those features.

browse.php?t=videos -> /category/videos/
browse.php?a=ronie -> /author/ronie/
details.php?t=script.foo -> /show/script.foo/