Use the project version.txt as fallback for SDK version

[dsblank]

Details

1. Use envionment "VERSION" if it exists
2. Else, uses version.txt file contents
3. Else, uses 0.0.1

Issues

Resolves #166

Testing

Tested all three scenarios

Documentation

None

[dsblank]

Also, makes it possible to install from other directories, like:

pip install -e sdks/python

which didn't work before.

[alexkuzmik]

@dsblank approved, but please run pre-commit run --all-files to fix lint errors (from sdks/python folder).