Fixed test cases, improved properties support for variants

Properties for variants:
- added displaying of properties set on variants to the Properties tab
- added handling of not set properties:
  If local property is added to variant's parent then variant doesn't have value for such property. 
With fixes from this pull request user will see empty values in the management panel for these unset properties. Also, in the product view, if there are variants with empty properties, such properties will be shown as empty value (in table or select box). If all variants do have property set, then no empty value will be shown. If specific property value is not used by any variant, then this value will not be shown in Select box for variants.

- fixes for seo templates