Correct the trouble on null return value for dumpTemplate method on Joomla 3.x

Change the call on template params.
The property _registry no more exists.
Need to use the toObject() method.
Apply one single change on dumpTemplate method to be compatible with JRegistry (Joomla 3.2) and the new Registry namespace (Joomla 3.3).

Check on Joomla 3.2 and Joomla 3.3, it 's ok with this patch.

(another small addon is in my Fork. Adding a param in the install URL of the plugin to auto-select the system folder : &filter_folder=system )