WIP: GoDaddy Contributions

Corrected generateModelDefinition() to scan for model references in remote accepts, returns, errors, and nested models
Changed addRoute() to honor X-Forwarded-Host
UI/UX cleanup for SwaggerUI
	Add support for toggling Model and Schema, instead of just expanding
	Added guard against null mockSignature
	Added support for toggling Model and Schema, and added support for primitives in StatusCodeView
	Changed to hide the message-bar when no message
	Changed to use defaultValue, if present, for sampleValue
	Changed to use relative path for images/throbber.gif for mounting into apps at different levels
	Collapse and label responseModel description by default
	Correct description of collections of object and nested
	Corrected to avoid showing invalid Model and Model Schema is missing or void
	Corrected to load images relative to swaggerRoot, for nested context root
	Corrected to work when loading resources from file://
	Ensure Response Content Type is shown regardless of Response Class
	Omit divs for info.title and info.description if they're absent
	Removed 'Implementation Notes' label since it's just noise, widened Resource expansion anchor to full label

**Tasks**
 - [x] https://github.com/strongloop/loopback-explorer/pull/58
 - [ ] `X-Forwarded-Host` header (#61)
 - [ ] `apiVersion` and `swaggerVersion` (#61)
 - [ ] UI customization (`contentWell`) (#61)
 - [ ] describe models for accepts and nested returns  (#61)
 - [ ] response and error messages  (#61)
 - [ ] additional param metadata like `pattern` and `enum`
@shelbys thanks for clarifying this, I presume it is up to us to submit the changes from your forks to the upstream repos and do any changes necessary to get the patches landed.

I am assuming the changes in swagger-ui and swagger-js are not tied to this pull request and thus can be upstreamed later, after this PR is resolved. Is that correct?

/cc @altsang @altsang I did not anticipate this task when estimating the effort, almost certainly I won't be able to prepare swagger-ui and swagger-js changes this sprint.