Deepreg: add changelog

[mathpluscode]

Subject of the documentation

Since the release of 0.1.0b1, we have fixed a few bugs and added a few features.

It would be nice to have a changelog. For now, we can do it manually,
and each PR into the main should update the changelog so that everything is tracked ;)

[mathpluscode]

Changelog 0.1.0b2

Added (for new features):

• Added option to change kernel size and a kernel type for LNCC image similarity loss.
• Added visualization tool for generating gifs from model outputs.
• Added log_root argument for training and prediction to customize the log file location.
• Added environment.yml file for Conda environment creation.
• Added Dockerfile.
• Added documentation about using UCL cluster with DeepReg.

Changed/Updated (for existing functionalities):

• Updated instruction on Conda environment creation.
• Updated TensorFlow version to 2.3.1.
• Updated the issue and pull-request templates to fix some
• Updated the pre-trained models in MR brain demo.
• Updated pre-commit hooks version.
• Updated references in JOSS paper to address reviewers' comments.

Deprecated (for soon-to-be removed features):

• None.

Removed (for removed features):

• Removed integration tests on training and prediction.

Fixed (for bugs):

• Fixed tensor comparison in unit tests and impacted tests.
• Removed normalization of DDF/DVF when saving in Nifti formats.
• Fixed invalid link in the quick start page.

[mathpluscode]

@zacbaum @s-sd @sbb-gh @zacbaum @acasamitjana @RemiDelaunay I've included our changes as above since the first release (acc to the PRs), the categories come from https://keepachangelog.com/en/1.0.0/.

I've tagged you as you have contributed to the package since then, did I miss anything?

@ebonmati @NMontanaBrown @YipengHu @MattClarkson What do you think about this kind of changelog ;)

[ebonmati]

Looks good to me