Dice Roller on Swift and Android should sync across platforms

[ultrasaurus]

The DiceRoller demo apps on Android and iOS currently only sync within their respective platforms. This is because DiceRoller on Android uses VOM as its binary format, while iOS simple sends a byte value across the wire.

So far, we have discussed three approaches to make DiceRoller sync cross platform:

1. Use VOM on iOS as the binary format. This can either be a fully fledged VOM-encoding, or a basic encoder that only supports integer values.
2. Use JSON on both iOS and Android. Both platforms include JSON serialization frameworks, but we have to plumb through the support to convert arbitrary objects to JSON (unless we limit the support to integers as well). There are already discussion in place (https://docs.google.com/document/d/17tAce1WC8SOe2kH8-sk_EGrvWN5IkKJTcqXKSJBCIUE) that describe this approach and its possible pitfalls.
3. Update Android to also use iOS's byte encoding.

We need to decide which road to go down on so that we can present a meaningful example app.

[ultrasaurus]

@schmidt-sebastian and I talk with @asadovsky and we think it would be expedient to go with #1 and start out supporting just integers & strings (and whatever basic types are needed for TODO if there are more)