PathFinder fix for add-ons with complex namespaces

In case of addons with complex namespaces we could get situation when $pathfinder->getURL() returns
/atk_formbuilder/././DSD\FormBuilder/templates/css/formbuilder.css

Resulting URL should be:
/atk_formbuilder/DSD/FormBuilder/templates/css/formbuilder.css

Fixes in this commit:
1. Fixed: Only first occurance of /./ was removed/, should remove all occurances.
2. Fixed: \ signs from complex namespace name should be converted to / in URL.
3. Some comments fixed.