Bugs email

Fixes #241 and #312.

By default, users will now have to enter a "From:" when sending screenshots or alarms via email.
The previous default values, e.g. "opi@css", didn't tell the recipient who sent the email, making it hard to reply.

Sites who want to use default 'From:' email addresses can add this to their site-specific plugin_customiation.ini (as before).