use actor for Gmail/IMAP/SMTP

[tomholub]

Then I'll merge this, and we make sure that we use actor for Gmail/IMAP/SMTP in another issue.

Originally posted by @tomholub in #1055 (comment)

[ivan-ushakov]

Since GTLRService has async functions and we use them, there is no need to have GmailService as actor.

[tomholub]

Got it. I assume same for IMAP/SMTP. Closing