Split Baseframe's third-party assets into a separate repo

[jace]

Baseframe's third-party asset collection messes with the commit history and content of this repository: committers get credit for code that is not theirs, and the repo appears to be mostly JS and CSS when the original content is mostly Python.

Third-party assets should be split out into an independent repository named baseframe_assets, with baseframe retaining an import hook to make them available as baseframe.assets.

[karthikb351]

Will you then use baseframe_assets as a git submodule inside baseframe?
That way you get a link between versions of baseframe and baseframe_assets and can safely update/rollback.

[jace]

I'm leaning towards totally independent packages:

1. Git submodules are confusing because they link to specific releases. Every update to the submodule will require an update to the parent repo.
2. We don't want to package assets into a PyPI release. Anyone using the source release should be able to install the other package to get assets.
3. Private assets such as commercially-licensed icons can now be in a private repo, imported into baseframe via an app-specified import hook.