Added alarm settings feature, modified other features

- Added an alarm settings content type. It is basically a content
  type that allows us to easily set up a repeating alarm. The
  repeating date api was not ideal for this application since it
  requires an end date, where a repeating alarm goes on indefinitely

- modified the sent field in the alarm feature to be an actual boolean
  rather than a text field

- Added an entity reference to the alarm content type so that it can
  refer back to the alarm setting that created it. This is done to make
  adding/removing alarms from an alarm setting much easier.

- images/icons were added to taxonomies. This will make it much
  easier to create our custom form for creating alarms.
Added 'answered' and 'card sent' fields to alarms

- Added a boolean answered variable to the alarm content type. This
  variable must be set to 1 to mark that a question has been
  successfully answered.
- Added an entity reference 'card sent' that should contain a nid
  of the flashcard node that has been sent.