Added Sources model + controller

commands:
rails generate redmine_plugin_model body_tracking source
project:references name:string description:text
rails generate redmine_plugin_controller body_tracking sources index
create destroy

db/migrate/002_create_sources.rb

@@ -0,0 +1,10 @@
+class CreateSources < ActiveRecord::Migration
+  def change
+    create_table :sources do |t|
+      t.references :project, index: true, foreign_key: true
+      t.string :name
+      t.text :description
+    end
+    add_index :sources, :project_id
+  end
+end