Gp2

Latest bug fixes for the UNet+ classifier, which is the classifier based on the original but with a few extra options. The bug was not allowing a user to use this classifier because it defines it's own build function but it was instead calling its super class build which uses the existing model.build which did not exist in this case.

- Pip Install Support: You can now install the GP2 Framework and its dependencies using pip. Just run `pip install gp2`.

- Performance Improvements: We've added support for additional UNet Classifiers.

- Minor Bug Fixes: We've resolved a few minor issues from the previous release.

Extended UNet support to Keras-UNet, Keras UNet Collection, and Customizable UNet. Added CNNPlus to discriminator support which is a customizable CNN discriminator.