Removed generation of __version__.py

Removed generation of __version__.py

It makes gbs fail when run from source tree, if version is not
generated yet. It also breakes tests because of the same reason.

I reimplemented it in a way that version is taken from __init__.py and
imported or parsed where version info is needed.
Note, that in setup.py and Makefile it's parsed in order to less depend
on python code. setup and Make should be able to work even if
__init__.py has syntax errors. The only requirements to get a version
from there is that it should be in parseable form.

Change-Id: I928d4c75f970345c6ccd7be2cc54e4f3d9d1df38