Switch record watching to kotlin coroutines #40

Record watching is currently implemented with RxJava.

The current implementation has a number of other problems:

• Watch events don't emit when it creates a directory in the course of creating a record #39
• Each resource watch can duplicate underlying path watches
• Data Session leaks watches when closed

I don't want to address these with the RxJava implementation. Take care of them in the rewrite based on coroutines.