As a user, I want to be able to create an account, so that I can have my data on multiple devices

[CharlieMcVicker]

• Handling upgrading anonymous accounts, option to sign in in settings page
• When a new user comes, ask if they'd like to continue as guest or make an account
• Banner on dashboard asking user to make an account

[CharlieMcVicker]

Upgrading account specs:
As a user with an anonymous account...

• I have the option to create a permanent account with Google or with email and password
  • If I pick email/password, an email+password form appears for me to create an account
• Afterwards...
  • If successful I see a "your account is now linked" message
  • If I get "credential-in-use" error, I get a sensible error message with steps to fix it
    • Give option to contact admin
  • Other error, give option to contact admin