zfit/zfit: Binned and sampling fixes

Many smaller fixes that are crucial, most notably to avoid a bias in sampling. Bug fixes and small changes create_extended added None to the name, removed. SimpleConstraint now also takes a function that has an explicit params argument. add name argument to create_extended. adding binned losses would error due to the removed fit_range argument. setting a global seed made the sampler return constant values, fixed (unoptimized but correct). If you ran a fit with a global seed, you might want to rerun it. histogramming and limit checks failed due to a stricter Numpy check, fixed. Thanks @P-H-Wagner for finding the bug in SimpleConstraint. Dan Johnson for finding the bug in the binned loss that would fail to sum them up. Hanae Tilquin for spotting the bug with TensorFlows changed behavior or random states inside a tf.function, leading to biased samples whenever a global seed was set