ResourceTreeModel: moved keyword matching code into ResourceItem class

Place functionality to where it belongs. ResourceItem::matchKeywords()
now returns whether a given list of strings matches with various
string properties of the item.

include/ResourceItem.h

@@ -212,6 +212,10 @@ public:
 
 	void reload();
 
+	// returns true if all given keywords match name, tags etc.
+	bool keywordMatch( const QStringList & _keywords );
+
+	// return true, if given ResourceItem is equal
 	bool operator==( const ResourceItem & _other ) const;
 
 	// rates equality with given item