Added support for multiple authentication schemes

To use the client credentials, index.html needs to have
1. input boxes to receive client id and client secret
2. handlers that intitialise OAuth correctly on change.

For example, you could replace the explore and apikey inputs in the header with:

      <div class='input'><input placeholder="client id" id="input_clientId" name="clientId" type="text" autocomplete="off"/></div>
      <div class='input'><input placeholder="client secret" id="input_clientSecret" name="clientSecret" type="text" autocomplete="off"/></div>

and add the following javascript to handle updates within the initialisation block (replacing the apikey javascript):

      function updateOauth(){
          initOAuth({
              clientId: $('#input_clientId')[0].value,
              clientSecret: $('#input_clientSecret')[0].value,
              realm: "blank",
              appName: "blank"
          });
      }

      $('#input_clientId').change(updateOauth);
      $('#input_clientSecret').change(updateOauth);

These examples could be incorporated into the swagger index.html file if required (or a new example created)

Issues - displaying multiple schemes could be improved.  Currently the UI is unaware that a particular scheme is required for a call so displays all scopes as options.  Will require work on core swagger ui and templates to make scheme available to swagger-oauth.js

Added support for multiple authentication schemes

To use the client credentials, index.html needs to have
1. input boxes to recieve client id and client secret
2. handlers that intitialse OAuth correctly on change.

For example, you could replace the explore and apikey inputs in the header with:

      <div class='input'><input placeholder="client id" id="input_clientId" name="clientId" type="text" autocomplete="off"/></div>
      <div class='input'><input placeholder="client secret" id="input_clientSecret" name="clientSecret" type="text" autocomplete="off"/></div>

and add the following javascrip to handle updates within the initialisation block (replacing the apikey javascript):

      function updateOauth(){
          initOAuth({
              clientId: $('#input_clientId')[0].value,
              clientSecret: $('#input_clientSecret')[0].value,
              realm: "blank",
              appName: "blank"
          });
      }

      $('#input_clientId').change(updateOauth);
      $('#input_clientSecret').change(updateOauth);

Need to clear out previous popupDialog nodes, so previous checkboxes won't be considered.

* Uses npm to download latest swagger-js (for now. When swagger-js is
   released we will replace git address with actual swagger-ui)

* Uses `postinstall` to generate `browser` folder of swagger-ui. This
 can go when swagger-ui is published.

Fixes #457

* For the e2e tests to run, we had to enable CORS in http-server.  The
  release of http-server that supports CORS hasn't come out yet so we
  have to use http-server@master until then.  Here is the commit I speak
  of: 30f4d1e008

Fixes #949

Fixes #949