Add RPC for "omni_sendtomany" and "omni_createpayload_sendtomany"

[dexX7]

The documentation for two new RPCs is added for send-to-many transactions:

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omni_sendtomany

Create and broadcast a send-to-many transaction, which allows to transfer tokens from one source to multiple receivers.

Arguments:

Name	Type	Presence	Description
fromaddress	string	required	the address to send from
propertyid	number	required	the identifier of the tokens to send
mapping	array	required	an array with the receiving address "address" and the "amount" to send

Result:

"hash"  // (string) the hex-encoded transaction hash

Example:

$ omnicore-cli "omni_sendtomany" 1 '[{"address": "37FaKponF7zqoMLUjEiko25pDiuVH5YLEa", "amount": "10.5"}, {"address": "3HsJvhr9qzgRe3ss97b1QHs38rmaLExLcH", "amount": "0.5"}]'

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omni_createpayload_sendtomany

Create the payload for a send-to-many transaction.

Note: if the server is not synchronized, amounts are considered as divisible, even if the token may have indivisible units!

Arguments:

Name	Type	Presence	Description
propertyid	number	required	the identifier of the tokens to send
mapping	array	required	an array with output index "output" starting at 0 and the "amount" to send

Result:

"payload"  // (string) the hex-encoded payload

Example:

$ omnicore-cli "omni_createpayload_sendtomany" 1 '[{"output": 2, "amount": "10.5"}, {"output": 3, "amount": "0.5"}, {"output": 5, "amount": "15.0"}]'