SW-130. Distribute simulation module variants, and select at install time


Changes include:
* Added --simhost option for SCons copy-simfw target. Copies current
  openwsn-fw simulation firmware to a 'linux' or 'windows' subdirectory of
  'sim_files' Renames the file to include CPU architecture, either 'amd64'
  or 'x86'.
* Added --nosimcopy option to SCons 'run' targets to avoid automatically
  copying cross-built simulation firmware in openwsn-fw.
* Updated setup 'install' target to select and copy the proper simulation
  firmware variant from the linux/windows directories, up to the
  'sim_files' directory. Implemented with a custom 'build_py' class that
  extends the setuptools default when building the package data directory.
  Exclude the firmware variant directories from installation.