Add ability to connect existing account to Google

[emranbm]

For current users, it's vital to be able to connect their current SahaBee account to their Google account, so can take the benefits of the future Google OAuth login feature.
For this reason, these features are needed, in order:

• Ability to delete account. So can undo any unintentional Google login.
• Ability to connect the current SahaBee account to a Google account. So that the future logins can be performed through Google.