Prevent enrollments in full sections

Until we get the waiting list feature done, just prevent people from
enrolling in a full section.
Remove parts when a section is removed

The Section model had a has_many relationship to a Part, but there was
no 'dependent: :destroy' option, so when a section was removed the
Part(s) were still hanging out.  This caused an error on the calendar
because it is driven by pulling all parts, and then working up through
the relations to get to sections and courses.  When a part doesn't have
a section, things get a bit wonky.

Also added 'dependent: :destroy' for the has_many :enrollments relations
on both the User and Section model.  The way I figure it, if a Section
is removed, it doesn't make any sense to have the enrollments hanging
out, same goes for when a User is removed.  They don't need their
enrollments either.
Merge pull request #6 from cit-jmu/prevent-enrollments-in-full-sections

Prevent enrollments in full sections
Merge pull request #8 from cit-jmu/fix-orphaned-section-parts

Remove parts when a section is removed
Setup New Relic for app monitoring

Add 'newrelic_rpm' gem and config file.  The license key was removed
from the config/newrelic.yml file and must be provided via the
NEW_RELIC_LICENSE_KEY environment variable
Explicitly set license key from environment var

The docs say that any environment variable starting with `NEW_RELIC_`
will automatically be picked up by the agent, but it doesn't seem that
way - at least not with the license key.  So I had to manually specify
it in the newrelic.yml file as `ENV['NEW_RELIC_LICENSE_KEY']`.

Also set the app name :)
Merge pull request #9 from cit-jmu/newrelic

New Relic for app monitoring
change cal invite email to cit@jmu.edu
Merge branch 'master' into order-section-list-by-date
Display available sections chronologically

Added a :starts_at virtual attribute to the Section model which pulls
the first :stars_at date from its parts.  Then we order the
@available_sections for display on the course#show page using this
virtual attribute.