[FEATURE]-Modify VideoCodecBase/CiscoSparkCodec to implement IRoutingSinkWithSwitching and IRoutingSource

[ndorin]

Is your feature request related to a problem? Please describe. Currently a codec behaves as though it is a routing midpoint by implementing IRouting, which is technically inaccurate.

Describe the solution you'd like Have the codec act as both a source and a sink. Route lists on source list items would need to specify multiple routes, one between the source and the codec and one between the codec and the display.

SourceRouteListItem needs to have a SourceListKey (string) property added so that routes can reference other source list items as prerequisite routes.

[ndorin]

After further discussion:

• Codec device should probably instantiate virtual source devices that implement IRoutingSource for each discrete video output the codec uses. These should be the devices that get routed to the display via whatever tie lines permit.
• Codec itself should implement `IRoutingSinkWithSwitching* only
• Consider adding a new object to the config structure at the level of sourceLists called routes where routes that might either be shared by multiple source list items or may need to be more verbosely defined can be defined in config.
• In rooms where the video codec acts like a switcher for both presentation and shared content sources, two separate routes need to be called in most cases. A route between the source and the correct input on the codec, as well as a route between the codec output(s) and the display(s)