use new tf api; use python 3; use relative paths

[de-code]

Not sure if you want to accept it. But at least for the two notebooks it is using the newer TF API, it is using Python 3 and relative paths.

It also fixes one of the variable naming issues - related to softmax. And addressed deprecated method using pydensecrf. I didn't update much text. There is no need to use a special branch or an old version of pydensecrf as far as I understand.