1475/1437 - Add fee elimination and update economics concepts

[ipopescu]

What does this PR fix/introduce?

This PR started with a recording from Ed, and the scope was to add new content describing what “fee elimination” is in Condor/Mainnet (task #1475). Since many other topics were covered and connected, I ended up updating more pages in the economics section, thus also addressing task #1437.

• added fee elimination content (c2226af90773bba166a0368f66632e7503b433f3)
• added dynamic pricing content (a4cc6bcfb6a4313d1fad45ebdebb958aebb93dca)
• updated existing content that was not relevant given the new Condor configurations (78c8c1d948565934e446cf1e26b803e1da06fe49)
• updated the economics pages (index.md, runtime.md, gas-concepts.md)
• updated a few entries in the glossary
• updated the chain-spec.md file to include the fee configurations. Took the opportunity to update all other entries, including the opcode-costs.md file

Closes #1475 Closes #1437

Checklist

(Delete any that aren't relevant)

• [x] Docs are successfully building - yarn install && yarn run build.
• [x] For new internal links I used relative file paths (with .md extension) - e.g. ../../faq/faq-general.md - instead of introducing absolute file path, or relative/absolute URL.
• [x] My changes follow the Casper docs style guidelines.

Reviewers

@ACStoneCL @AlexanderLimonov FYI @EdHastingsCasperAssociation

[ipopescu]

I'll merge this PR so that it gets ported. If we need to make changes, @AlexanderLimonov, we can open a new PR.