Cleaning & conventions for Substrate module 5 - Post UCB

[nuke-web3]

WIP

Part of #761

TODO

• Migrate code into dedicated repo(s) for Substrate module  #718 with help from @kianenigma 🙏
• Fix images under new convention broken in other modules using same img. (followup)
• update README with more faculty facing details ala https://github.com/Polkadot-Blockchain-Academy/pba-content/blob/5b5f99d809b4e15348104b7c6e43da6f95a4a1b7/syllabus/1-Cryptography/README.md

[kianenigma]

Happy to merge this sooner to avoid conflicts once I start to make content changes.

[kianenigma]

Migrate code into dedicated repo(s) for Substrate module #718 with help from @kianenigma 🙏

Suggest this to be done separately as it is more involved.

[kianenigma]

merging this as-is to avoid conflict with any further work.

[kianenigma]

This is half finished, so I will revert it again, sorry.

@nukemandan I will leave this asset refactoring up to you.

TBH I think the old structure is fine. What I recommend doing instead is #855