Adds minor fixes:

- Added appropriate imports:
  - from okota.token_index.index import to_identifier
  - from cic_eth.error import SignerError
- cleaned up balance func.

apps/cic-eth/cic_eth/eth/erc20.py

@@ -22,7 +22,7 @@ from hexathon import (
 from chainqueue.error import NotLocalTxError
 from eth_erc20 import ERC20
 from chainqueue.sql.tx import cache_tx_dict
-from okota.token_index import to_identifier
+from okota.token_index.index import to_identifier
 
 # local imports
 from cic_eth.db.models.base import SessionBase
@@ -46,13 +46,14 @@ from cic_eth.task import (
 from cic_eth.eth.nonce import CustodialTaskNonceOracle
 from cic_eth.encode import tx_normalize
 from cic_eth.eth.trust import verify_proofs
+from cic_eth.error import SignerError
 
 celery_app = celery.current_app
 logg = logging.getLogger()
 
 
-@celery_app.task(base=CriticalWeb3Task)
-def balance(tokens, holder_address, chain_spec_dict):
+@celery_app.task(bind=True, base=CriticalWeb3Task)
+def balance(self, tokens, holder_address, chain_spec_dict):
     """Return token balances for a list of tokens for given address
 
     :param tokens: Token addresses