Remove trailing slashes from paths and header parameter improvements

[kanadgupta]

Adds the following (with corresponding tests):

• Removes trailing slashes from the paths when operations are created
• Overrides Accept header types found in response definitions if an Accept header is sent in the form data
• Added a $ref lookup to path operation parameters

Asana tasks:

• https://app.asana.com/0/681252538274980/1108254356757915/f
• https://app.asana.com/0/681252538274980/977151049856241/f

[domharrington]

Yo! String.prototype.endsWith isn't supported in ie11. Can you check to see if this works in ie11? I can give you access to our browserstack account. I'm hoping that we've got @babel/env setup correctly here:

api-explorer/.babelrc

Lines 3 to 7 in 7963c65

	["@babel/env", {
	"targets": {
	"browsers": ["last 2 versions"]
	}
	}],

but it's possible that we need to add an exclusion to allow ie11.

[kanadgupta]

I'd be happy to test it in IE11 or just refactor this to something more universally compatible too. What would you prefer?