Add Colored Coin feature

[azuchi]

Introduce the following Colored Coins feature to support the issuance and transfer of arbitrary tokens on Tapyrus.

• English: https://gist.github.com/azuchi/712bf84bd01c8e181b2377233ef9952a
• Japanese: https://gist.github.com/azuchi/8fff51de048c6fced31531544583fff2

[Naviabheeman]

Implementation tasks

• CScript and script interpreter changes for new OP code - OP_COLOR
• Consensus checks for OP_COLOR transactions and blocks
• New RPC/API to get color identifier from a UTXO
• Wallet support for maintaining Token balance - it could be multiple tokens, should we use separate wallets for each type of token?
• Wallet support to send, receive and burn tokens.
• GUI - show separate Token balances, send, receive and burn
• wallet RPCs - show separate Token balances
• functional tests involving all types of tokens and all operations
  • check wallet balances
  • check block and transaction validation.

It maybe useful to create new RPCs to:

• get all tokens available in the blockchain (present and burnt)
• get token summary for a particular token (issued block/time, present ownership, balance)

[azuchi]

get all tokens available in the blockchain (present and burnt)

maybe tokens can be included in existing getbalance RPCs.

[Naviabheeman]

I added Colored coin support in Tapyrus Wallet page to describe the changes required. Please review and comment if something is missing.

[Naviabheeman]

GUI code - #200, #201, #202, #204, #205