Qualifier references

add support for qualifier and reference suggestions. 
Personally, I would try to stick to the pseudo selectors. Though it's a little bit more of a hassle, I would assume those to be more "stable":
```
$claimview = this.element.closest( ':wikibase-claimview, :wikibase-statementview' );
claimview = $claimview.data( 'claimview' ) || $claimview.data( 'statementview' );
if( !claimview ) {
  return false;
}
return this.element.closest( claimview.$qualifiers ).length > 0;
```
As for an <code>_isReference</code> function: Shouldn't <code>this.element.closest( ':wikibase-referenceview' ).length > 0</code> do the job?