Experimental cmake helper for generic ros_lib generation.
Better generic CMake helpers.

Using arduino-cmake submodule from myself, pending this merge:
https://github.com/queezythegreat/arduino-cmake/pull/96
Fix copyright on lib script.
Clean up rosserial_arduino/package.xml

- Removed unnecessary build_depends on message packages
- Added run_depend on arduino-core, per
  https://github.com/ros/rosdistro/pull/5610
Only pass TOOLCHAIN_FILE when specified.

Also don't pass the package path, since it's unnecessary. Avoiding
unused variables suppresses a CMake warning.
Remove submodule, add arduino-cmake as non-submodule.
Merge pull request #138 from ros-drivers/cmake_helpers_rebased

CMake Helpers