Minz: remove url_rewriting

As suggested
https://github.com/marienfressinaud/FreshRSS/issues/163#issuecomment-38478669

At the same time, removes a bunch of (almost) dead code such as
Minz_Router (the few remaining lines being moved to Minz_FrontController
to avoid a class)

Contributes to https://github.com/marienfressinaud/FreshRSS/issues/303