sim: embedd background bmp and load from memory

Loading the file from disk introduces a slight dependency on the working
directory for the simulator. Prevent that by loading the bmp from
memory.

Use a python script to convert the backround bmp image to a C header
file. Include this header in `main.cpp` and load the bmp from memory.

CMakeLists.txt

@@ -325,6 +325,10 @@ endif()
 
 target_include_directories(infinisim PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/gif-h")
 
+# embedd background image for the status window to use
+add_subdirectory(img)
+add_dependencies(infinisim infinisim_img_background)
+
 install(TARGETS infinisim DESTINATION bin)
 
 # helper library to manipulate littlefs raw image