Added Quantities model and controller

commands:
rails generate redmine_plugin_model body_tracking quantity
rails generate redmine_plugin_controller body_tracking quantities index
create destroy

app/controllers/quantities_controller.rb

@@ -0,0 +1,11 @@
+class QuantitiesController < ApplicationController
+
+  def index
+  end
+
+  def create
+  end
+
+  def destroy
+  end
+end