New onboarding pages, polymer paper elements

* New onboarding pages for uProxy
 * Initial splash page
 * Description page
 * Get / Share choice (buttons currently just advance to next screen, will take effect once we re-implement modality tabs)
 * New network login page (moved from networks.html to splash.html)
* Polymer paper (material design) elements
 * New grunt task to compile paper-*.html elements by moving their inline scripts to a separate .js file (inline scripts are not allowed in Chrome extensions)

Tested in UI (chrome popup), re-ran "grunt test"
I called them first and second because the first line can actually be either userName or userId (depending on whether or not userName is available).  userNameOrId and userId as class names seem less clear