Csbdeep

Maintenance release with various smaller changes:
- Fix issue when using TensorFlow 2.13.0
- Support Python 3.11
- Re-activate `h5py` version pin when using TensorFlow 1 (i.e. installation via `pip install "csbdeep[tf1]"`)
- Update isotropic reconstruction notebook
- Fix smaller issues in example notebooks

Maintenance release to remove pin of `h5py` version (see [CSBDeep 0.6.2](https://github.com/CSBDeep/CSBDeep/releases/tag/0.6.2)).
(There still *might* be h5py-related issues when using TensorFlow 2.4 or earlier, which is not recommended.)

Bugfix release pinning `protobuf < 3.21` to be compatible with TensorFlow 1.x.
(Only if CSBDeep is installed via `pip install "csbdeep[tf1]"`.)

Cf. https://developers.google.com/protocol-buffers/docs/news/2022-05-06#python-updates

Bugfix release to be compatible with old versions of Keras (cf. [failed legacy tests](https://github.com/CSBDeep/CSBDeep/actions/runs/2360006291)).

Minor changes, but now only supporting Python 3.6 or later (i.e. dropping Python 2.7 and 3.5).
- Fix several deprecated uses of other packages (distutils, scipy, numpy, tifffile, keras)
- Other minor changes

Maintenance release to support TensorFlow >= 2.6.0, which (again) depends on a standalone Keras package (see [release notes](https://github.com/tensorflow/tensorflow/releases/tag/v2.6.0)).

Since CSBDeep supports TensorFlow 1.x (which always needed a separate Keras package) and TensorFlow 2.x (which never required a separate Keras package until version 2.6.0), we are forced to change the installation instructions:

- *Unchanged* when using TensorFlow 2.x: `pip install csbdeep`
- *Updated* when using TensorFlow 1.x: `pip install "csbdeep[tf1]"`