UI elements code clean up

In order to maintain some consistency in UI elements before the release, do some code formatting clean up:

• remove wrapping function and “use strict” from UI elements.
• fix indentation.
• move <script> code blocks inside <dom-module> as a good practice.

https://www.polymer-project.org/2.0/start/first-element/step-2
"At the end of the element definition is some JavaScript that registers the element. If the element has a <dom-module>, this script is usually placed inside the <dom-module> to keep everything together."