Add the ability to view review conversation for published records

[tmorrell]

Is your feature request related to a problem? Please describe.

Currently there is not an easy way to view the community request conversation for published records. You can search in closed community requests for a record, and then click through to see the conversation. But this is an annoying multi-step process.

Describe the solution you'd like

@ugswork has added a tab to published records with the conversation that shows up for record owners or admins, and made the code available at https://github.com/ugswork/published_record_conversation. I've tested it and it works well, and believe it should get added to the core in some form.

Open questions:

1. Should the conversation tab be the default, or should it be configurable?
2. How much community-specific code should go into app-rdm (records.py changes)?

[tmorrell]

One bug in the @ugswork implementation is that the conversation tab also shows up in the request record preview, where it doesn't work. It's also not needed in that view since there is already a tab for conversation.