2.5 Guestbook Sendmail

- Using google api sendmail, taskqueue, ndb.transactional
- After commit a greeting successfully, send a notification email
from greeting sender
to a specific email address (abc@....)
Fix comment

import wrong lib
Add username to body email
Fix comment

- underscore user_email
- “if users.get_current_user():” instance of “”if
users.get_current_user() is not None:”
Merge pull request #10 from nhathv/feature/sendmail

Merged pull request #10　send mail