quickfix for tf 2.2

Created by: scarlehoff

I was playing with the release candidate of TF 2.2 (https://github.com/tensorflow/tensorflow/releases/tag/v2.2.0-rc3) and I noticed a crash when passing tensor content to the compile function. To be 100% honest I am not sure whether this is a bug or not (since it is a rc) but I figured out it didn't make much difference to change it and actually removes some deprecated calls that were left.

There are a few changes in TF 2.2 which will surely be incorporated to n3fit, but those will have to wait until it is released and default everywhere. Basically some of the overrides in MetaModel.py which are there because of inconsistency within TF/Keras have been fixed (yey!)

About the changes to regression tests, I honestly don't know what to do to have some consistency there. Right now they work with up to 4 decimal places in my computer but fail in Travis (because of the second decimal place). This is a separate issue but anyway.