Deleted all 3dr python dependencies (broken commit).
Added support pip (with and without virtualenv).

Added pip.json syntactic sugar.

Refactoring

Supressed pylint warnings.

Added 'pkg_name' option for packages whose 'pip name' does not match with pkg name.

Ignore all global packages from sys.path.

Added *.dist-info to ignore list.

Fix https://github.com/pypa/pip/issues/1439 (added '--no-use-wheel' option).
Now all dependencies are not resolved by default.
Simplify code.
Reformat code.
Rename "install_venv" function.
Refactoring - extracted "create_virtualenv" function.
Simplify code.
Simplify detection of GAE directory.
Fix detection of GAE directory on Windows.
Simplify code.
no missing venv workarounds, pip install -r used, libx for manual libs

This commit reduces complexity of the pip install process of
requirements by always depending on virtualenv which allows us
to use pip install -r requirements.txt.
Manually installed libs in main/libx are not touched but have
precedence.
Added libx to sys.path.
Removed double insert libx.
Simplified if.. else.. statements.
Removed unused code.
Small refactoring of "exec_pip_commands".
Removed excess string formatting.
Removed excess formatting of strings.
Added main/lib to .(git|hg)ignore.
Unset global PYTHONPATH for virtualenv.