OSMF SVN

Removing obsolete import statement.

Removing obsolete import statements.

Applying HTML support prerequisite refactorings:

* Making 'gateway' of type IMediaGateway a property on media element.
* Adding a GatewayChangeEvent, removing RegionChangeEvent.
* Removing RegionTargetFacet and setRegionTarget utility function.
* Adding IMediaGateway, and IContainerGateway interfaces.
* Adding a 'gateways' package, and moving RegionSprite into it. Removing the 'regions' package.
* Updating framework client code, unit tests and sample code accordingly.

Add ProxyElement for handling VAST Impressions.

Add missing override to unit test.

Use MockHTTPLoader for testing BeaconElement, to isolate unit tests from network.

Add Beacon and BeaconElement framework classes, for integrating tracking requests with MediaElements.

Last set of unit tests for ListenerProxyElement.

More unit tests for ListenerProxyElement. Required some minor API changes to SwitchableTrait, to enable triggering of the indicesChange event.

Documentation bug FM-85.