XD-479 Add Conversion to Channel Registries

XD-479 Add NoOpRedisSerializer

Fix up adapters to not use toString() if payload is already byte[]
and the valueSerializer is a NoOpSerializer.

Clone the SI publishing adapter to do the same.

Still doesn't do any real conversion, just to/from String and byte[] (TODO).

XD-479 Add Inbound and Outbound Conversions

- port @dturanski 's JsonRedisSerializer, removing Redis and
    renaming to TypedJsonMapper

- outbound conversion passes byte[] without change and uses the
    TypedJsonMapper for other payloads. The local transport
    performs no outbound conversion.

- inbound conversion uses the TypedJsonMapper to get back to the
    original object; if the sink doesn't support the type, attempt
    to use the conversion service to convert to a supported type.

- Add a boolean property (default true) to the LocalChannelRegistry
    that controls whether any conversion is attempted.

Add tests
XD-479 Polishing

Increase test coverage on conversion code.

Add sendAndReceive test to AbstractChannelRegistryTests
XD-479 Polishing (PR Comments)

Also, MediaTypeTests didn't actually test anything.
Merge branch 'XD-479' of git://github.com/garyrussell/spring-xd into garyrussell-XD-479