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

test/unit/quantity_test.rb

@@ -0,0 +1,9 @@
+require File.expand_path('../../test_helper', __FILE__)
+
+class QuantityTest < ActiveSupport::TestCase
+
+  # Replace this with your real tests.
+  def test_truth
+    assert true
+  end
+end