* Update proto file with Tx 'estimated gas used' field
* Update tx_counter according to tx gas quota
* Feature/user spam limit checks (#47)
* Print proof generation error before sending it
* Check user spam limit in grpc send_transaction endpoint
* Add initial code for handling multiple merkle tree in UserDB
* Add unit test for multi tree
* Add test_new_multi_tree unit test
* Introduce UserDbConfig