Propose transaction based on Payroll policy

[johnnyluo]

Based on a defined policy , Payroll plugin need to propose transaction , and then send the transaction to verifier server to sign it.

• Parse a plugin policy
• Based on the policy rule to decide whether it is time to propose a new transaction
• construct the transaction
• Send the transaction to verifier server to keysign with it

[webpiratt]

Progress of sub-tasks could be tracked by Tx Indexer issue label

[RaghavSood]

Done in #100