Add some new stuff.

* Support for playing audio on new alert. Custom sounds specified by the user not supported.
* Fixed a number of validation errors and typos in the HTML files.
* The background and popup pages now properly sync the number of new alerts that have popped since the popup was last opened.
* Fixed an issue with the alerts management related to platform switching.
* Split the Lotus symbol out from the background image to allow for easier resizing of the popup window should the need arise.