[N/A] Channel model bugfixing

[bryangaleopenfin]

Fixes more bugs in Channel Model revealed by integration tests

• A window could be listed as being part of two channels
• When querying windows in channels, we would return whatever had been passed to us previously rather than a sanitized Identity object

[MichaelMCoates]

If we're concerned about a bad identity passed here, should we have an identity.name !== undefined check here?

[bryangaleopenfin]

For the purposes of the prototype, I'm not concerned about bad identities, and that's probably a thing to check outside of this anyway

[bryangaleopenfin]

The sanitizing is more just so that the data we send out is 'clean', and doesn't mean anyone's given us a bad identity. It was primarily motivated to make test-writing easier, but it feels like the the 'right' thing to do anyway

[pjbroadbent]

Yeah, we'll eventually do the sanitising at the client/APIHandler level, rather than having to put that kind of thing all over the provider.

Doing it here is good for the time being, though.