Update for recent btcjson API change.

This commit updates the Tx field of the ListReceivedByAddressResult to
TxIDS to mirror the recent change btcjson.
Refactor txToPairs into smaller functions

Also adds tests for those functions, and improve fee estimation.
Make scrypt parameters overridable/optional
Move new addrmgr Options type and default to top.

Default values near the top of the file is preferrable so they are more
easily spotted.
Expose functions needed from the voting pool package