Support invite accept reject

[James-Mart]

Description

This PR introduces two important improvements for user management:

1. The invites generated in the invite plugin can now be accepted/rejected. If accepted, a new account is created.
2. Transactions submitted on behalf of accounts that require key authorization will automatically sign with the necessary keys.

Changes overview

• Create the producer account specified at boot as a real account on the network
• Improve invite plugin
• Add initial plugins for all auth services: authsig, authany, authinvite, authdelegate
  • ...of these, authdelegate is still just a skeleton. Accounts using authdelegate will fail to send transactions.
• Improve smart-authorization docs
• Separate the smart-auth interface used by auth plugins (the export interface) from those that need to dynamically link to the user's auth plugin (the import interface).
• Develop dynamic plugin loading infrastructure (to allow transact to dynamically link to the user's auth plugin and auth notifiers)
• transact plugin: attach correct claims/proofs to each transaction
• Add "logout" and "isLoggedIn" functions to accounts plugin
• Significant refactor/cleanup of supervisor plugin loading code. Loads plugins in two phases:
  • Phase 1) Load all "regular" plugins (not dynamic)
  • Phase 2) Load all dynamic plugins (those that are linked to dynamically)
    • This phase separation is necessary because loading dynamic plugins may depend on calling into prior loaded "regular" plugins to retrieve information

[James-Mart]

Was tempted to just put this in transact/plugin/deps/. I figured leaving it next to export.wit will help ensure that these stay in sync