[#139] Fix /transactions/addresses endpoint return

[brunodb3]

• Fixes the issue with /transactions/addresses endpoint
  • The indexing was not behaving properly due to an error implementing AwaitLock
  • AwaitLock was getting stuck when multiple listeners were activated, so the data was never saved to the database
• Fixes/moves leveldb connection handling of errors on .get method
  • Instead of throwing an error when value is not found, returns an empty list. This was done on the leveldb.service previously, but a better place is on the leveldb.connection, as it covers more use-cases
• Some identation and linting fixes

---

closes #139

[brunodb3]

Tested with redis, the error only happened with leveldb. PR is good to go.