initial commit of wait-list feature

The basic wait-list feature.  Added a boolean attribute 'waiting' to the
Enrollment model to track whether a user is waiting or actively enrolled
in a section.  Then had to retroactively update everything that broke :)

This is just a rough commit, there's still some refactoring and cleanup
to do, but it serves the basic waiting list functionality.

- If a section is full the [Enroll] button changes to [Wait for a spot]
- The section#show view shows the Course Roster and Waiting List
- The stats#enrollment dashboard indicates the # of people waiting
- The users#show page 'current_enrollments' section indicates courses
  you are waiting on.
turn off mail delivery in development
add wait list button to calendar#index
fix up enroll/wait list links on section pages
Tidy up enroll/drop/wait list buttons

It's still kinda fugly, but I don't have a better way to do things now.
At least it's a bit more organized and less spaghetti-fied.
Promote waiting enrollments on destroy

When an enrollment is destroyed and there is room in the section, the
waiting list will be checked and an enrollment will be promoted in the
order that they are on the waiting list.
apply waiting icon

Use the waiting icon in the course titles, sections, and calendar.
save after sign in location for sections#wait_list

add the :wait_list action to the :store_custom_after_sign_in_location
before_action callback.
Merge pull request #18 from cit-jmu/wait-list

Waiting lists