TCR Pallet Tutorial

[JoshOrndorff]

In the old substrate.dev there is an outdated tutorial to write a TCR dApp. https://substrate.dev/docs/en/tutorials/tcr/ This old tutorial is deprecated and will not be ported directly to the new site.

The code has been mostly updated and the new code lives at https://github.com/substrate-developer-hub/tcr-substrate . This issue is to finish updating the code and write a tutorial about just the pallet, not the UI.

Tasks

• Update code to alpha.6
• Improve on_finalize to call two separate helper methods for expiring applications and polls.
• Write the tutorial

Followup task: A separate tutorial about about writing the front end. See #5