Create build_distrib.py tool to automate creation of all possible distribution packages

[cztomczak]

Build all at once. This script should do the following:

1. Expects that all supported python versions are installed
   a) On Windows search for Pythos in the root directory
   and in %localappdata%\Programs\Python
   b) On Mac use system Python 2.7 and Python 3 from ~/.pyenv/versions/
   directory
   c) On Linux use only Pythons from ~/.pyenv/versions/ directory
2. Expects cef_binary*/ directories from Spotify to be in the build/ directory
3. Install and/or upgrade tools/requirements.txt
4. Run automate.py --prebuilt-cef using both Python 32-bit and Python 64-bit
5. Pack the prebuilt biaries using zip on Win/Mac and .tar.gz on Linux
   and move to build/distrib/
6. Build cefpython modules for all supported Python versions on both
   32-bit and 64-bit
7. Make setup installers and pack them to zip (Win/Mac) or .tar.gz (Linux)
8. Make wheel packages
9. Move setup and wheel packages to the build/distrib/ directory
10. Clean temporary directories

[cztomczak]

Done in commit e9db0e8.