Email address

Fixes #1191

- Adds an alert box when someone changes their email and $modSettings['send_validation_onChange'] is set.
- Moves out the validation message to its own action.

The new text string needs better wording:

$txt['email_change_logout'] = 'You decided to change your email. You will be logged out. Please reactivate your account.';

And the page title probably shouldn't be $txt['profile']

Any suggestions?