Use express routes instead of modifying remoting.

This completes the migration of swagger processing from strong-remoting
into loopback-explorer.

Added additional usage instructions to README and additional testing.

This commit introduces a change into where resource descriptors
are hosted. They are no longer hosted under /swagger, but instead
under the same path as the Explorer, wherever that may be.
Generally, the resource listing will be available at
/explorer/resources, and api listings under
/explorer/resources/{modelName}.