Update Basics to new design scheme using Jade extends/blocks

[chalin]

• overview - docs(dart): update BASICS intro #1410
• architecture - docs(architecture): proofread, updated Dart app #1807
• displaying-data - docs(guide/displaying-data): proofread #1819
• user input
• forms: TS and Dart versions have diverged too much
• dependency-injection - docs(dependency-injection): revise Dart and TS code and prose #1573
• template-syntax - docs(template-syntax): review and update Dart to new doc design #1465
• cheatsheet
• style guide (no Dart version yet)
• glossary - docs(glossary): general cleanup and fix links #2100

Contributes to #1506.

[wardbell]

Please hold on this project!

[chalin]

Please hold on this project!

Ok. FYI, I am almost done (95%) with the dependency-injection chapter. I'll commit on Tuesday. Will hold off working on the other chapters until I hear news from you.

cc: @kwalrath