package: update devDependencies

 - loopback 1.x to ^2.4.1
 - mocha ~1.20.1 to ^1.21.5
 - supertest ~0.13.0 to ~0.14.0
Merge pull request #62 from strongloop/run-tests-agains-loopback-2x

package: update devDependencies
swagger: use X-Forwarded-Host for basePath
swagger: Deprecate `opts.swaggerVersion`

Users of loopback-explorer should not override the swagger version,
as it's the explorer who decides what version of the Swagger Spec
it implements.
loopbackStyles: improve spacing in small window

Improve spacing of page elements when the browser window is small.
swagger: include models from accepts/returns args

Models not attached to the app are included too.
route-helper: add `responseMessages`

Add a default "success" response message, the status code is 200 or 204
depending on whether the method returns any data.

Append any error messages as specified in the `errors` property
of method's remoting metadata.

Include error message models in the API models.