Testnet RC-0.2.0

Fresh off of Pocket Summit 2.0, things are starting to ramp up. As the team gets leaner and more organized, a focused excitement spreads over the company. Mainnet development has begun and the roadmap is clear.
Release Candidate 0.2.0 contains the long awaited Challenge Request, allowing clients to make nodes accountable for their responses.

• Renamed RelayProof to Proof (in JSON)
• Renamed Invoice (memory) to Evidence
• Renamed StoredInvoice (blockchain persisted) to Receipt
• Renamed ProofWaitingPeriod to ClaimSubmissionWindow
• Changed RPC and from node-proof to node-receipt
• Update posmint module to use sdk.Ctx interface
• Fix pseudorandomGenerator unexported properties would return empty json
• Evidence now holds proof interface to allow for challenge proofs
• Added Relay Request Hash (Hash of payload + meta) to RelayProof object
• Added Block to Dispatch Request
• Added Relay Meta field to relay request
• Added Challenge Functionality
• Added Challenge Request to RPC
• Changed dispatch response to an actual structure and not just a session
• Added block height to dispatch response
• Removed all MustGetPrevCtx and used PrevCtx for panic safety
• Changed receipt structure (added evidence type)
• Change querySupplyResponse struct to use totalStaked, totalUnstaked & Total as *big.Int due to memory overflow
• Added RPC SPEC doc in yaml and json with swagger support