Switched the visibility from protected to public on a couple of methods
- Adapter::getProduct and Adapter::productExists are now public.
Minor bugfixes on the Attributes importer
- Allow strings as $features in the Attributes::addFeatures method
- Attributes::addSingleQuantity() now allows "0" as a valid quantity
The CSV Reader translates a field with a single dot as an empty field
Enhancements to the Product Importer
- Added the `disableFreeProducts()` and `isActiveProduct()` methods.
- Rewrote the main query on the `disableUnusedCategories()` method.
- Minor bugfix on the `normalizeCategories()` method.
  The PS_ROOT_CATEGORY and PS_HOME_CATEGORY ids are now ignored when
  a default category is assigned.