Restructure codebase

[fhenneke]

We decided to restructure the code to make it easier to maintain and extend.

The general structure would be as follows:

• Data collection via APIs which are encapsulated in classes, e.g., Web3API, OrderbookAPI
• Data processing in tests; each test has its own class and depends on different APIs for fetching data
• unit tests and end-to-end tests using mock instances for the data fetching

It might be possible to make those changes one by one, without breaking the code.

TODO:

• implement prototype for iterating on the design
• move all data fetching to API classes
• convert all monitoring tests into new format
• add unit tests and e2e tests