Updates opentok service with new events

• Removed checks for existing subscriber on stream created event
• Added on stream destroyed event listener in opentok service
• Added on audio changed event to opentok service

Added new media related event listeners to opentok service

Methods added:

• onClosedMediaAccessDialog
• onAudioLevelUpdated
• onMediaAccessAllowed

Removed rxjs and @types/node from dependencies

Rxjs was causing problems with npm link because it was added in the node_modules of the library installed in other apps.

These dependencies have to be in the devDependency section to be installed when doing npm link or npm install from the root of a package, and can be managed like any other npm configuration param