Upgrade from Python2.7 to Python3

Hi, I am Vasudev and very much interested in Machine Learning particularly Deep Learning R&D. Your open source software **Fabrik** is pretty much valuable and impressive to both researchers and a novice in the field of AI. I would like to contribute in this project.

I would like to mention a small improvement

Since **Python 2.7** will reach the end of its life on January 1st, 2020 and it wouldn't be maintained afterwards, I think Fabrik should be upgraded to **Python3**. Though I didn't check out it's compatibility with **Python3**, it maybe also that it's working perfectly well with **Python3**.

I have some minor suggestions which might be relevant: -
**TODO**
- [ ] To upgrade from `Python2.7` to` Python3 `as it is maintained by the community.
- [ ] Document changes regarding the same.

Thanks!