Implement (and release) the new generated content branches

[tkw1536]

• for each repository there should be exactly one generated content branch
• it should always be one commit ahead of the master
• should be forced pulled / pushed by lmh

/cc @m-iancu @kohlhase

[m-iancu]

Just continuing the discussion. After discussing with @florian-rabe we agreed to have 3 branches:

1. master (for backwards compatibility) can have any generated content is needed for that archive (or none at all) -- e.g. florian might want to commit and version some generated files for experimental archives. 2.sources which is versioned but contains only sources, can be used by users or systems which generate their own content (e.g. MathHub) 3.generated which is unversioned (force-pushed) and has all generated files (and sources) for a complete deploy-able version. Can be given to externals to quickly have a running system.

A lot of branch management can be done just by adequate .gitignore (ignoring the correct folders for sources and master branches). For the rest we need lmh support. I started a template archive at https://gl.mathhub.info/meta/template based on the lmh none template.

[tkw1536]

I would recommend against having any branch that is both versioned and has generated content on it (i. e. master) as this would increase the repository size dramatically. I would suggest we only have sources and generated. The people who really need generated content can just use the generated branch.

[m-iancu]

As mentioned above, master is only for backwards compatibility and @florian-rabe prefers it for specific archives. That makes transition easier, without breaking existing workflows. Otherwise I agree in principle we should slowly move away from that. But there are archives for which generation takes a lot of time/effort and only have a new version once a year, so versioning each of them might not be a bad idea.

[kohlhase]

I agree, space is cheap. Let's go with this setup for now.