Add v2 inputs

[chris124567]

• Add v2 siacoin and siafund inputs
• For v1 inputs, store a reference to the siacoin_elements or siafund_elements integer ID instead of the encoded parent ID
• Fix bug with when inserting into siacoin and siafund elements tables. To get a mapping of element IDs to integer IDs in the database, we would use result.LastInsertId() in addSiacoinElements/addSiafundElements, which worked the first time an element was inserted, but not when it was updated to reflect spent status (it would return the latest ID in the table rather than the elements ID). This did not cause any issues until now because this would only occur when an element was spent (ie when the element was an input in that block), and for inputs we were storing the encoded parent ID rather than the numeric ID from the database, so the incorrectly mapped IDs were not used anywhere. Now we use RETURNING id at the end of the query so the ID reflects the element we actually want.