* Lists ROMFS files explicity instead of using GLOB_RECURSE

Previously, when ROMFS files that were not airframes were touched, the ROMFS
would not be rebuilt. The ROMFS files are now specified explicityl in a
CMakeLists.txt file that is located in the root ROMFS directory.

Now when one of the ROMFS files is touched the whole ROMFS is rebuilt.

When new files are added to the ROMFS, they need to be explicity added to
the CMakeLists in the ROMFS root directory.

* ROMFS: adds individual CMakeLists files in each subdirectory

Also moves the temporary ROMFS build directory to ${PX4_BINARY_DIR}/ROMFS/genromfs
so that the cmake_install.cmake files and the CMakeFiles directories (generated whenever
are not add_subdirectory() is called) are not generated in the temporary ROMFS directory
from which the ROMFS binary is created.

* cmake ROMFS generate add px4_add_romfs_files function

* ROMFS CMakeLists: adds explanatory comment to px4_add_romfs_files function

* ROMFS CMakeLists: updates copyright headers

* NuttX cmake

* px4_macros:Pass the stringified predicate as second arg to static assert

   CC_ASSERT mapes to the c++ static_assert or provides the same
   funtionality for c via the other macros. The c++ static assert
   takes 2 argumants the prdicate and a message. This fixes the
   lacking second argument.

* Updated nuttx and apps submodule to upstream nuttx 7.21+==master

   This is the latest uptake of upstream nuttx and apps.

* ROMFS generate with xxd instead of objcopy

* delete nuttx-patches

* NuttX update submodules to latest px4_nuttx-master

* fix nuttx apps and board dependency

* docker_run update to latest container 2017-08-29

* cmake ROMFS portable sed usage

* NuttX update submodules to latest px4_nuttx-master

This is the new interface to control external LED's (user-facing).
Features:
- Supports maximum N Leds (where the board can define N)
- on/off/blink M times
- Different priorities
- Allows setting a single led or multiple at once

It makes more sense to set the optimization flags on a platform basis
instead of individually for each module. This allows for different
optimization options for SITL, NuttX, Snapdragon, etc.

Now the mixer is a C++ library that can be fairly easily bolted into an output driver to provide mixing services.

Teach the FMU driver how to use it as an example.  More testing is still required.