[typescript-rxjs] runtime and api cleanup

Created by: denyo

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
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Description of the PR

This PR simplifies models RequestArgs and ResponseArgs and makes them an alias for { AjaxRequest, AjaxResponse } from 'rxjs/ajax';. Also parameter names make more sense now and unneeded checks are removed. For people that have previously applied any middlewares this is breaking due to the model changes but it is quite easy to fix. Docs where also extended.

Middleware Before

export class AuthInterceptor extends Configuration {
  private static config: AuthInterceptor;

  private constructor() {
    const middleware: Middleware[] = [
      {
        pre: (context: RequestContext): RequestArgs => ({
          ...context,
          options: {
            ...context.options,
            headers: {
              ...context.options.headers,
              Authorization: `Bearer ${getAuthToken()}`
            }
          }
        })
      }
    ];

    super({ middleware });
  }

  public static get Instance() {
    return AuthInterceptor.config || (AuthInterceptor.config = new this());
  }
}

Middleware After

export class AuthInterceptor extends Configuration {
  private static config: AuthInterceptor;

  private constructor() {
    const middleware: Middleware[] = [
      {
        pre: (request: RequestArgs): RequestArgs => ({
          ...request,
          headers: {
            ...request.headers,
            Authorization: `Bearer ${getAuthToken()}`,
          },
        }),
      },
    ];

    super({ middleware });
  }

  public static get Instance() {
    return AuthInterceptor.config || (AuthInterceptor.config = new this());
  }
}

@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10)