Upgrade user auth to use Pow

[eliknebel]

• Replace core hand-rolled authentication system with Pow (https://hexdocs.pm/pow/README.html)
• Add JS client side refresh to fix live view issues (Instructions for WebSocket usage (e.g. Phoenix Channels and LiveView) pow-auth/pow#271)
• Convert user session over to use Pow
• Fix link_account and create_and_link_account functions
• Re-add social login support using Pow assent (https://hexdocs.pm/pow_assent/README.html)
• Investigate change route paths for pow to match existing routes
• Implement Password Reset, Email Confirmation, Email Invitation, and Welcome Email
• Add "Remember Me" persistent sessions (https://hexdocs.pm/pow/pow_persistent_session.html)
• Change author first_name last_name fields to use standard OIDC values
• Dynamic header link (authoring vs delivery)
• Fix social login account linking
• Re-enable captcha
• Account link fails when user input has an error or redirect to other pow links (e.g create account)
• Should create and link account require user email confirmation?
• Use name field for display in favor of family/given fields since name will already be formatted based on locale (https://openid.net/specs/openid-connect-basic-1_0.html#rfc.section.2.5)
• Add multi-role support to author
• Fix theme selection
• Customize flash messages
• Find and fix TODO's
• Fix unit tests
• Check/update social provider Authorized redirect URIs