OAuth2 OpenID Connect provider support, API and DB refactoring (#3)

Allows Paskia to authenticate the user to a client site.
- User friendly client registration flow on the admin app
- Redirect-based authentication flow (per spec)
- Backchannel logout both ways to keep sessions synchronized
- Groups integrated with Paskia's permission system
- Adds email, preferred username and telephone fields on user profile
- All new user basic info layout to show the new information, better looks
- API and DB structures redesigned
- Various unrelated fixes to theming and layout

frontend/src/components/RemoteAuthPermit.vue

@@ -771,7 +771,6 @@ defineExpose({ reset, deny, code, handleInput, loading, error })
 .input-wrapper {
   position: relative;
   display: flex;
-  width: 280px;
   max-width: 100%;
 }