email: add auto fetch attachments for POP3 accounts

This change adds an option to allow auto fetch the complete POP3 message.

Change-Id: Id92a46a8f84a575160f04003f72dfe513441d356
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
email: hide send feedback menu if feedback uri is empty

Feedback uri is not set for stock email app. Just hide the menu if the
send feedback uri is empty.

Change-Id: I8f65975124ecf6c415ebf2e64da68bbdd5430b94
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>