Support RailsAdmin Property class
Support RailsAdmin Property class

Refs. https://github.com/sferik/rails_admin/commit/875c9ba7c18665f768bc48f118c0e9d0c74cb81a

janx/rails_admin_jcrop,enjoycreative/rails_admin_jcrop,ack43/rails_admin_jcrop,billguy/rails_admin_jcrop,ack43/rails_admin_jcrop,ack43/rails_admin_jcrop,enjoycreative/rails_admin_jcrop,ack43/rails_admin_jcrop,enjoycreative/rails_admin_jcrop,enjoycreative/rails_admin_jcrop,billguy/rails_admin_jcrop,billguy/rails_admin_jcrop,janx/rails_admin_jcrop,janx/rails_admin_jcrop