disable brush pressure averaging, implement single finger for camera rotation when touch draw is disabled

src/canvas.h

@@ -115,7 +115,7 @@ public:
     static Canvas* I;
     NodeCanvas* m_node = nullptr;
     bool m_alpha_lock = false;
-    bool m_touch_lock = true;
+    bool m_touch_lock = false;
     glm::mat4 m_mv{ 1 };
     glm::mat4 m_proj{ 1 };
     glm::vec4 m_box{ 0 };