Add config option base_path, used when generating local URIs behind reverse proxy

addresses #527
- useful when running behind a reverse proxy
- for consideration/discussion only.  I actually don't advocate this
- instead of having a base_url string to prepend to URIs, a more flexible approach would be a local_url() mapping function
- since it is targeted at node-http-proxy, it fixes generated URIs but does not change the routes listened for.
- there is a corresponding pull request for Casper
- there is a corresponding pull request for connect-slashes

fix {{url}} helper
fix jslint issues
more path fixes