CMS-2007 Facet refactoring

All facet related components are moved to api_facet module.
All component names are changed to be the same as in java code:
Facet to TermsFacetEntry, FacetGroup to TermsFacet, added
Facet interface. FacetContainer was renamed to FacetGroupView
Merge pull request #346 from enonic/CMS-2007

CMS-2007 Facet refactoring