0.19.0 release planning

[agriyakhetarpal]

Hi all, this is a tracking issue for planning the next release.

PRs to be included, so far:

• Add ConfigLoader with deduplicated logging and try_examples config caching #249
• Better mobile device detection for interactive examples buttons #250
• Update documentation around fullscreen usage of jupyterlite-sphinx apps #253

[agriyakhetarpal]

The release is up, on:

• PyPI: https://pypi.org/project/jupyterlite-sphinx/0.19.0/
• conda-forge: https://anaconda.org/conda-forge/jupyterlite-sphinx/files?version=0.19.0

Thanks for helping with the release, @steppi!