Introduce `rake cms:import` task to import data

Usage: `rake cms:import DATA_DIR=<path_to_your_data_dir>`

rakefile

@@ -159,3 +159,15 @@ end
 task :publish => :package do
     sh("scp #{BUILD_DIR}/#{NORMALIZED_DEPLOY_NAME}_#{PKG_VERSION}*.deb #{PACKAGE_REPO}")
 end
+
+namespace :cms do
+  desc "Import course data within the given DATA_DIR variable"
+  task :import do
+    if ENV['DATA_DIR']
+      sh(django_admin(:cms, :dev, :import, ENV['DATA_DIR']))
+    else
+      raise "Please specify a DATA_DIR variable that point to your data directory.\n" +
+        "Example: \`rake cms:import DATA_DIR=../data\`"
+    end
+  end
+end