SW-74. Added pip support; reworked tree-based setup.py to use setuptools

After we upload OpenVisualizer to PyPI, a user will be able to use
'pip install' to download and install OpenVisualizer and its
Python-based dependencies.

Detailed changes:
* Renamed treeSetup.py to setup.py as the standard setup routine.
  nativeSetup.py is for development use only.
* Added PyDispatcher and bottle to top-level requirements.pip.
* Removed PyDispatcher implementation from eventBus directory.
* Added install_requires parameter to setup, with contents of
  requirements.pip. Save a copy of requirements.pip to openvisualizer
  data directory since it must be read when user installs.
* Updated README.txt to reflect pip-based installation.
* setup.py-based install now logs to appropriate directory;
  Windows -- user's AppData\OpenWSN
  Linux ---- /var/log/openvisualizer
* Added SCons target to upload to PyPI.