Send email without blocking
Swap to gmail sending

Uses the new gmail address for sending out vote information
Merge branch 'upstream' into develop
Handle mass-emailing

Adds the field to take email addresses of invitees, and sends an email
to each.

Field values are newline-separated.
Factor out email sending to another class

Creates the MailSender class to send an email from the voting.app@gmail.com
address to a provided email with the provided subject and message.

We also go back to using concatenated strings instead of the verbatim
string, because the verbatim string messes up the indentation by adding
whitespace at the beginning of indented lines.
Use static constructor for MailSender

We only need to set up the SmtpClient once, so we use a static constructor
Merge pull request #51 from tpkelly/develop

Invite to poll