GPcounts upgraded version with code restructure

This version of GPcounts supports tensorflow version 2.15.0 and gpflow version 2.9.0.

The paper results can be found on tag 1.0.0.

Full Changelog: V1.0.0...V2.0.0

GPcounts first version

GPcounts version used to re-reproduce the results described in the paper "Non-parametric modelling of temporal and spatial counts data from RNA-seq experiments".