Require valid proofs from ticketing service to write to the ledger

[mattcollier]

See FIXME:

veres-one-validator/lib/validators/proofs.js

Lines 12 to 15 in cdd493c

	// TODO: in testnet v2, the `AuthorizeRequest` proof on the operation
	// is only validated using json-schema. For v3, use jsigs.verify to properly
	// validate the signature
	module.exports = async ({basisBlockHeight, ledgerNode, validatorInput}) => {

Related FIXME/TODO are found in the test suite.