Add `Mocking Service` button to menubar

  - add new menu item, `Mocking Service` button, to menu bar
  - use one of CSS3 checkbox styles to make button look really nice and
    modern; sizing and positioning are glitching from time to time though
  - add `mockingService` AngularJS service to work with remote mocking
    service
  - add tests for `mockingService` service
  - add `mockingService` controller
  - add tests for `mockingService` controller
  - fix `saveMeta` so that it resolves to passed meta, not file
  - cleanup `Gruntfile.js` and add support for CORS proxy as `/proxy/`
    when running `grunt server` for development
  - make a full copy of json object and store it for selected file
    before we broadcast `event:raml-parsed` event because console
    modifies and makes it unusable for mocking service
  - use spinner to give users a feeling that we're handling their
    requests and system is at work
  - hide Mocking Service on/off button when file is not parsable as for
    shelf and console
  - do not store RAML and its JSON in meta as we do not use it and it
    wastes a lot of space and has issues with localStorage limit
  - add tests for replacing original `baseUri` with mocked one
  - add `Beta` tag to `Mocking Service` control