Perform general code refactoring

[tiabc]

7. In many places we use switches over the three networks we support (mainnet, ropsten, rinkeby). This may be meaningful to move them into a separate interface encapsulating common operations for these networks and created by a factory.
8. I believe transactions sending and deciding which server to use for it deserve better architecture. Let's examine if concerns are separated correctly and fix it if not.
9. Make jail.baseJSCode always end with ; somehow. Those ugly hacks adding ; to the end are annoying.
10. Investigate why we return 0x address in case of a missing value in RPCCall.ParseFromAddress.
11. ExecutionPolicy should be an interface and an appropriate implementation should be set in construction time, not during execution. Hence less checks for config.UpstreamConfig.Enabled. Generally, all logic regarding RPC requests handling must be incapsulated in small components which complies to a single interface, this shouldn't be handled with if statements for different cases.
12. preProcessRequest and postProcessRequest should be named appropriately and shouldn't be just hanging functions.
13. Probably, it should be not StopRPCCallError which callees return but callers should instead detect an error and terminate if it's fatal or something.
14. Revisit Jail, NodeManager and so on and determine concerns of each.
15. Search for StatusIM under vendor/go-ethereum and fix logger dependency for Status components which must come from geth/log. Tackle it only no earlier Wait for CompleteTransaction or DiscardTransaction for requests to the upstream server #245
16. StatusAPI's TxQueueManager and SendTransaction are only exposed for tests and look like either a design shortcoming or test helpers. Either way, this should be fixed after tests for C bindings are made separate from testing application logic.
17. TxQueueManager should not know about AccountManager and NodeManager. However, it should be able to send a transaction (after receiving CompleteTransaction() call). Refactor TxQueueManager and TxQueue #338
18. Refactor TxQueue and TxQueueManager handlers as after moving it to status-go, their purpose is unknown. Refactor TxQueueManager and TxQueue #338
19. Remove common.QueuedTxID. Refactor TxQueueManager and TxQueue #338
20. Refactor logging, some ideas are presented in this discussion: Fix log levels and enable ethereum-go logger #256, the main point is that NodeConfig.LogLevel seems redundant.
21. Remove node.RPCClient.
22. Bring NetworkId from NodeConfig together with UpstreamConfig as they are tightly coupled and this would decrease chances that they're inconsistent to one another.
23. Refactor NodeManager's all start and stop methods. Start/Stop logic is overcomplicated with synchronisation and has bad naming.
24. Think about creating RunningNode field in NodeManager which will eliminate a lot of unneeded checks.
25. Rename geth/jail/jail_cell.go to geth/jail/cell.go
26. Get rid of makeSendHandler call in geth/jail/handlers.go. It's post-refactoring byproduct, just use jail.Send instead.
27. Get rid of ExecutionPolicy.
28. Rename upstream to remote.
29. Remove faucet cmd, we now use an original geth node to request ether.
30. Fix lint notice for NodeManager type name will be used as node.NodeManager by other packages, and that stutters; consider calling this Manager

Subtasks will be added up until there is enough work to start.
TODO: Split this issue over several each taking approximately 1 day.
TODO: Traverse the source for TODOs and FIXMEs for other refactoring notes.

[tiabc]

Moved to https://www.notion.so/status/Refactoring-notes-f0ef9658543b4e149243153aa7d63eba
as this is not an issue and rather a collection of something we don't really care about.