Modify implementation of how data tables define cells

* We want a clean, clear, but flexible interface for using data tables
  * We want the model to define our cell
  * We want to be informative to the user if they do not define the cell

lib/project/pro_motion/data_table_screen.rb

@@ -1,12 +1,17 @@
 module ProMotion
   class DataTableScreen < TableScreen
+    class << self
+      def model(value, scope=nil)
+        if value.method_defined?(:cell)
+          @data_model = value
+          @data_scope = scope || :all
+        else
+          raise "#{value} must define the cell method"
+        end
+      end
 
-    def self.cell(cell)
-      @cell = cell
-    end
-
-    def self.cell_properties
-      @cell
+      def data_model; @data_model; end
+      def data_scope; @data_scope; end
     end
 
     def table_data
@@ -15,47 +20,20 @@ module ProMotion
       }]
     end
 
-    def cell_properties
-      self.class.cell_properties
-    end
-
     def cell_data
-      return [] if cell_properties.nil?
       return [] if data_model.nil?
 
-      data_model.send(data_scope).collect do |c|
-        if c.respond_to?(:cell)
-          c.cell
-        else
-          {
-            cell_class: cell_class,
-            properties: properties.inject({}) do |hash, element|
-              hash[element.first] = c.send(element.last)
-              hash
-            end
-          }
-        end
-      end
+      data_model.send(data_scope).collect(&:cell)
     end
 
     private
 
-    def properties
-      @properties ||= cell_properties[:template].reject do |k,v|
-        k == :cell_class
-      end unless cell_properties[:template].nil?
-    end
-
-    def cell_class
-      @cell_class ||= cell_properties[:template].nil? ? nil : cell_properties[:template][:cell_class]
-    end
-
     def data_model
-      @data_model ||= cell_properties[:model]
+      self.class.data_model
     end
 
     def data_scope
-      @data_scope ||= cell_properties[:scope] || :all
+      self.class.data_scope
     end
   end
 end