Custom Order Fields: Default value for select boxes is now stored

Issue #16
Identified places where ajax CSRF token validation could fail
Custom Order Fields: The regexp field now hides when an unsupported type is selected

Issue #16
Custom Order Fields: Duplicate select options are no longer permitted
Custom Order Fields: Fixed an issue where select options would not be properly removed

Issue #16
Custom Order Fields: Fixed an issue where the delete alert displayed incorrect info

Issue #16
Custom Order Fields: Implemented proper checkbox type support

Issue #16