Account Merge Functionality

[cycomachead]

• Should be able to join omniauth and LTI accounts
• Signing into an LTI account should try to find a 'regular' account
• Should signing into an account through non-LTI search for LTI accounts?

[cycomachead]

By merging user tables this is mostly obsoleted. Uses emails as the unique key.

Will do some testing and update if this is satisfactory enough for now, though true multiple identities could be useful.