BUG: Fix access to static configuration variables

- Make statics private
- Use Config::get rather than eval to read private statics
- Add a helper function to expose UserDefinedForm_EmailRecipient::$summary_fields
  (to make them available for i18n).
Fixing allowed_actions to private for SS 3.1 compatibility
Merge pull request #107 from oddnoc/fix-statics

BUG: Fix access to static configuration variables