Make landscape banners full-width

Set currentContentSizeIdentifier in landscape mode per 
https://developer.apple.com/library/ios/documentation/userexperience/Conceptual/iAd_Guide/BannerAdvertisements/BannerAdvertisements.html
Merge pull request #405 from TwoScoopGames/fix-landscape-banners

Make landscape banners full-width
Improved DOM API, cleaned up some variable naming

* HTMLElements now have get/setAttribute methods
* Load events can be added or removed via the
 .add/removeEventListener API
* Load event provides a shell event object for script tags
* .getElementsByTagName actually searches for the appropriate tagNames
* .tagName is now uppercase, like it is in a browser
Merge pull request #409 from amadeus/eject-js-updates

Improved DOM API, Cleaned up some variable naming