Clean up models by removing CDN specific ones / make their specific stuff settable

[jeroen]

There's two cases in which CDNs are simply derivatives of default streaming formats:

1. HTTP streaming with a slightly different start parameter:
   • bitgravity (starttime)
   • edgecast (ec_seek)
   • flvseek (fs)
   • lighttpd (start)
2. RTMP streaming with a SMIL file for load balancing:
   • highwinds
   • vdox

Removing these models and adding flashvars for these settings cleans up a lot of code. We need the following flashvars, with their defaults:

• http.startparam (undefined)
• rtmp.loadbalance (false)

Of course we shouldn't break backward compatibility. Therefore, a translation array should be introduced to translate the CDN types to their parent types, also setting the correct flashvars. The logic for that should reside in the controller (getModelType). The list for that can be put into AbstractModel or another model helper class.