Consolidated Exits support

[Pongch]

enabling JS-Starter-kit to have a minimal, albeit initially unsafe path to allowing a user to perform consolidated exit. This entails:

1. a user merge UTXOs that they have on the child chain
2. a user calling startStandardExit() on Root chain for that singular UTXO
3. a user performs processExit()
4. a user performs a re-deposit on a new chain.

Typing this out, I can see that the gap between processExit and redeposit part will be quite hard to perform from the UX perspective...or not.

Note: This feature will be temporary and will change once Ari and omg-js has support for /tx.create endpoint.

CC @kevsul