[#1475] Adopt transaction data requests

[LukasKorba]

Closes #1475

• RustBackend extended for the new 2 rust methods 'transactionDataRequests' and 'setTransactionStatus'
• lightwalletservice extended to add a new method 'getTaddressTxids'
• Enhance action has been refactored to handle transactionDataRequests
• Error codes for specific rust and service errors defined
• Checkpoints added
• Code cleanup

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[nuttycom]

The only problem I see is the Int64 being used for the address request end height.

[nuttycom]

utACK ad30b24