Store user language preference in profile
This is a continuation of work done in !1220 (closed) by @nsaikiran-guest . There are many changes, please feel free to squash them. I have fully reviewed this but wanted another quick eye from someone else.
- Fixed the history of the earlier pull request.
- Auto save profile when user model is created.
- Decouple language selection from login/logout code.
- Minor updates to model.
- Use Django's philosophy where we were deviating.
- Styling.
- Remove language selection from system->config.