Modify RestAdapter to own the whole URL space

Add urlNotFound middleware converting all unhandled requests into
a 404 error. This way to the express app created by
RestAdapter.createHandler always returns consistent error responses
and also prevents other parts of the application from creating
a URL clash.
Merge pull request #24 from strongloop/feature/handle-404-in-rest-url-space

Modify RestAdapter to own the whole URL space