Clean up loadBlocksFromNetwork function in modules.loader

[SargeKhan]

Expected behavior

The flow of the function should be more understandable and code should follow proper naming conventions.

Actual behavior

The function adds a lot of obscurity in the understanding of the functionality, it jumps control flow in multiple ways and is missing useful comments.

Steps to reproduce

Look at function implementation

Which version(s) does this affect? (Environment, OS, etc...)

All versions.

[MaciejBaj]

The syncing process refactor will be tackled separately. Right now it's not clear how it behaves, like sending ids of "first 5 blocks of (n) last rounds, descending order" through rpc.blocksCommon but establishing if nodes are sharing the same chain only by checking the first one of them:
https://github.com/LiskHQ/lisk/blob/development/modules/transport.js#L528.
Functionalities of sync process will be revisited and the corresponding issue will be opened. This issue is suspended for now and will become a part of the bigger sync refactor not to waste the efforts for cleaning up the function that might potentially be replaced in the near future.