Added measurement, readout and readout_value models

commands:
rails generate redmine_plugin_model body_tracking measurement
name:string hidden:boolean source:references
rails generate redmine_plugin_model body_tracking readout
measurement:references quantity:references unit:references
rails generate redmine_plugin_model body_tracking readout_value
readout:references value:decimal taken_at:timestamp

app/models/measurement.rb

@@ -0,0 +1,2 @@
+class Measurement < ActiveRecord::Base
+end

app/models/readout.rb

@@ -0,0 +1,2 @@
+class Readout < ActiveRecord::Base
+end

app/models/readout_value.rb

@@ -0,0 +1,2 @@
+class ReadoutValue < ActiveRecord::Base
+end