Added new four new convenience methods and tests

First two methods filter with isMemberOfClass:
-(NSArray*)subviewsMatchingClass:(Class)aClass;
-(NSArray*)subviewsMatchingClass:(Class)aClass
                        maxDepth:(NSInteger)depth;

Second two methods filter with isKindOfClass:
-(NSArray*)subviewsMatchingClassOrSubclass:(Class)aClass;
-(NSArray*)subviewsMatchingClassOrSubclass:(Class)aClass
                                  maxDepth:(NSInteger)depth;

Unit tests were added for all four methods.