LILY-300: restore/delete emailaccount after auth problem
LILY-300: complete refactor of:

- IMAPClient raises connection error if connection fails on init
- If no client is set on IMAPClient, login returns False
- No more session storage of email_auth_update
- Correct (active)emailaccounts are used in tasks
- Util functions for checking imap/smtp credentials
Merge branch 'feature/change-email-password-300' into develop