Webpack config prod/dev split

EDUCATOR-1448

Modifies paver webpack task to use production configuration in all
non-devstack environments, and a development config in devstack.

cms/envs/devstack.py

@@ -48,6 +48,9 @@ STATICFILES_FINDERS = [
     'django.contrib.staticfiles.finders.AppDirectoriesFinder',
 ]
 
+# Load development webpack donfiguration
+WEBPACK_CONFIG_PATH = 'webpack.dev.config.js'
+
 ############################ PYFS XBLOCKS SERVICE #############################
 # Set configuration for Django pyfilesystem