added filter builder widget and filter tree

filter builder takes filter options from user, then adds
completed filters to the filter tree. the filter tree does
not currently do anything. in the future it will filter the
cards in the database view.

cockatrice/src/cardfilter.cpp

@@ -0,0 +1,31 @@
+#include "cardfilter.h"
+
+const char *CardFilter::typeName(Type t)
+{
+	switch(t) {
+		case TypeAnd:
+			return "and";
+		case TypeOr:
+			return "or";
+		case TypeAndNot:
+			return "and not";
+		case TypeOrNot:
+			return "or not";
+		default:
+			return "";
+	}
+}
+
+const char *CardFilter::attrName(Attr a)
+{
+	switch(a) {
+		case AttrName:
+			return "name";
+		case AttrType:
+			return "type";
+		case AttrColor:
+			return "color";
+		default:
+			return "";
+	}
+}