[TASK] Improve integration friendliness for custom ConfigurationProviders

This change makes two aspects more safe: getTemplatePathAndFilename is now safe with an EXT:… file path set in the Provider - and getTemplateVariables will now always return an array (unless a subclass fails and returns NULL which will yield a PHP warning).
Merge pull request #182 from NamelessCoder/templatepath

[TASK] Improve integration friendliness for custom ConfigurationProviders