Create Remote Entity Connection Abstraction

[wmiaw]

MslControl currently accepts InputStream, OutputStream, or the MSL Url types for communication with the remote entity. Maybe this should be abstracted through some sort of remote entity connection interface, because it may be necessary to "close" and "open" connections for each MSL message or request/response pair.

This may be problematic for 3-message transactions, and due to expectation that a MslChannel is established and can be used for full-duplex communication. It may be that introducing this abstraction would be a bad idea because it breaks the expectation that an underlying protocol should be full-duplex and that overlay protocols like MSL should be agnostic. HTTP is the odd one out in that respect.