Completed 'Find Invite Details' story
Completed tests&code for Invite update API functions

* Fixed a bug in factories_spec.rb by removing some
  duplicative require statements

Did the following functional tests:
* allows me to delete an invite
* allows me to change the available quantity
fixed a problem with updating expires_at;now allows you to set to not expire by setting update value to '0'
Fixed bug in models' constructor

initialize was overriding the status values that were
already stored in the database. I wanted to default all
new models to have a status of "active", but the Sequel
constructor was causing the models to be overriden with a
value of "active" even if a value of "disabled" was already
set in the database.  I fixed this by adding an "if" statement
which prevented the assignment if the value was already
populated in the database.
Fixed minor bugs. See detailed notes for more info.
* Fixed bug in Invite model.
   - Changed '(expires_at.nil? || Date.today > expires_at)' to
     '(expires_at.nil? || Time.now > expires_at)' due to Ruby throwing
     an error when trying to compare Time (expires_at) to Date
* Fixed bug in API "Get Invite Detail" function
   - Added exception handling for instances where an invite does
     not exist or is deleted. Previously, it was just returning a
     string reading "null". Now it returns a 400 bad request error.