Added sql to insert signatureDueNotRated for emailing

EV-185

In addition, changes to the Mailer, AppraisalsAction,
Appraisal classes and Email properties were made. The
AppraisalsAction class now checks if it is appropriate
to send an email to the upper supervisor.
Added some extra logic to account for possible null values

EV-185
Added description and tests for isRated()

EV-185