module: add a common module base class with usage printf methods

Provides:
- thread-safety for module start/stop
- some shared code for module start/stop. Should also be less prone to
  errors.
- constructor & destructors are called from within the new module thread
- can be used for work queue & thread modules
- strutured & formal way for module printf usage & module documentation

Limitation:
- supports only modules with one instance (eg. not mavlink)

src/platforms/common/CMakeLists.txt

@@ -41,6 +41,7 @@ set(depends
 px4_add_module(
 	MODULE platforms__common
 	SRCS
+		module.cpp
 		px4_getopt.c
 		shutdown.cpp
 	DEPENDS