docs: final review of light client developer guide

[tmsdkeys]

Description

Final review of the light client developer docs. Made some corrections/changes:

• fixed order of modules/core/exported in a few instances
• moved setup.md to the end as it makes more sense imo
• combined the section on ClientMessage with the one one handling updates and misbehaviour as they respond to the ClientMessage, it looked cleaner
• moved upgrade.md before proofs.md
• Made upgrade.md easier to read by moving some text around and adding sections
• added some content in proofs.md as there was a circular referencing with client-state.md
• added a code block to proposal.md
• fixed the vuepress config as there was an incorrect ordering
• other stylistic changes performed by @crodriguezvega

Commit Message / Changelog Entry

docs: final review of light client developer guide

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[AdityaSripal]

Nice cleanup!

[tmsdkeys]

Potential additional changes to consider:

• Now that we discuss upgrade handling for light client devs in the light client dev guide, we should likely remove it from the 'upgrades' section of the docs? Maybe just add a link...
• in client-state.md some methods in the interface are not listed. don't know if this is on purpose? UpdateStateOnMisbehaviour, UpdateState, CheckSubstituteAndUpdateState and VerifyUpgradeAndUpdateState are missing

[damiannolan]

Thanks @tmsdkeys! LGTM

[crodriguezvega]

Potential additional changes to consider:

• Now that we discuss upgrade handling for light client devs in the light client dev guide, we should likely remove it from the 'upgrades' section of the docs? Maybe just add a link...

I removed the text that was there and added a link to the section.

• in client-state.md some methods in the interface are not listed. don't know if this is on purpose? UpdateStateOnMisbehaviour, UpdateState, CheckSubstituteAndUpdateState and VerifyUpgradeAndUpdateState are missing

I added a comment in client-state.md to clarify that not all methods of the interface are listed there and some methods are explained in detail in other sections.

[crodriguezvega]

Great work, @tmsdkeys!