disallow/undo rotation at low zooms and near world edge

src/map/transform_state.cpp

@@ -115,13 +115,20 @@ float TransformState::getAngle() const {
 }
 
 
-#pragma mark - Rotation
+#pragma mark - Changing
 
 bool TransformState::isChanging() const {
     return rotating || scaling || panning;
 }
 
 
+#pragma mark - Interactive
+
+bool TransformState::isInteractive() const {
+    return interactive;
+}
+
+
 #pragma mark - (private helper functions)