#5304 gateway: fix issues related to use of level db

• drop level-party
• upgrade level to version 8.0.0 and make changes to the code as necessary from the changes to the level library
• improve unit testing for all things that use level
• stop using production level files for testing. Now it uses temporary files that unit tests creating for testing.
• add a database.yml config file that defines the paths to the databases
• add reference counting to make sure objects using the database are only deleted when there are zero references

Link: https://github.com/hummingbot/hummingbot/pull/5304