function createAndInjectTag (tagObj) {
    if (!tagObj || tagObj.exists()) { return; }

    tag = createTag(tagObj);
    if (!tag) { return; }

    if (headScriptEl) {
      headScriptEl.parentNode.insertBefore(tag, headScriptEl);
    } else {
      headEl.appendChild(tag);
    }

    headTags.push(tag);
  }
Injects the necessary metatags in the document for mobile support:
1. Prevent the user to zoom in the document.
2. Ensure that window.innerWidth and window.innerHeight have the correct
   values and the canvas is properly scaled.
3. To allow fullscreen mode when pinning a web app on the home screen on
   iOS.
Adapted from https://www.reddit.com/r/web_design/comments/3la04p/

@param {object} scene - Scene element
@returns {Array}