separate pen mode and camera in different modes to be composed, start implementing line draw mode

android/CMakeLists.txt

@@ -39,6 +39,7 @@ add_library(
 	../engine/app.cpp
 	../engine/brush.cpp
 	../engine/canvas.cpp
+	../engine/canvas_mode.cpp
 	../engine/log.cpp
 	../engine/action.cpp
 )