Refactor tutorials/exchange_single_node.html

I find this very confusing
https://dev.bitshares.works/en/master/bts_guide/tutorials/exchange_single_node.html

I think lots of it got lost in translation, but it would also make sense to review this content wise. I find it hard to understand.

Thougts on the TOC and some pointers on the content from my side, built out as we go:

1. Introduction
What is this about? External exchange listening in on the blockchain for deposits/withdrawals, talk about last irreversible block and stuff
2. Requirements and Environment
Software/Hardware requirements
3. Setup
Running one normal node, delayed node or processing lib and whatnot (cli wallet, python or js backend on abstract high level), how everything should be setup (as system services, or docker, or something)
4. Watching accounts
Best practice to listen to events on the blockchain
4.1 Processing deposits
Listen on external database/blockchain for incoming deposits, and broadcast the issue/transfer operation
4.2. Recognizing withdrawal requests
Listen to incoming blocks on specified account with memo and act accordingly in external database/blockchain
5. References

Old docs had this (also not complete): https://dev.bitshares.works/en/master/bts_guide/tutorials/exchange_single_node.html#others

Thougts?
@abitmore @oxarbitrage @jmjatlanta @xeroc