In an effort to speed up loading times, removes all lazy loading of
related objects in `models.py` and resort to explicit loading.

## Logging In & Navigation
### Updates & Improvements
- External Login information is removed from the main User object and
only loaded when a user access their Profile page under a new
`/me/external-logins` endpoint.

## Threads
### Updates & Improvements
- New error management code will surface more errors, especially those
encountered before the thread is created.