If a user tries to export and we don't have an email for them, show them this error message

First, change the word "Account" to "Log out" in the Settings page.

Then add this notification when the user presses the export button but we don't have their email:

```
Hi!  

We'd love to send your measurements, but we don't have your email address. 

To add your email, please:
1. Go to Settings and press Log out
2. Login with Google
3. Try exporting again
```
