Don't freeze python_payload, freeze python_modules instead

manifest.py

 include("micropython/ports/esp32/boards")
-freeze("./python_payload")
+freeze("./python_modules")

python_modules/hello.py

+# remove me once we have something meaningful to put here
+print("hello world")

python_payload/boot.py

+# This file is executed on every boot (including wake-boot from deepsleep)
+#import esp
+#esp.osdebug(None)
+#import webrepl
+#webrepl.start()
+import main