Stop copy-paste, use git properly

[pinkwah]

A major problem that plagues komodo is that we keep multiple versions of every package and release, requiring us to copy-paste a non-insignificant amount of text every time we want to add a new version or komodo release.

I propose that we instead use git branches and stop having duplicate versions of releases.

Changes:

• master branch is for upgrade proposals only
• bleeding branch is used to build bleeding only
• Release branches (eg. 2020.06) are created by each respective RM, basing off of master.
• Only two release YAML files exist in any branch -- py27.yml and py36.yml.
• Bumping a package is just changing the values in repository.yml and the two release files.
• A new git tag is a new release that Jenkins picks up and builds.
  • Alternatively, there is a RELEASE_PREFIX file at the root of each branch that contains eg. 2020.06.rc2 -- the name of the release. This string, combined with the YAML release file (eg. py27.yml) is used to create the full name: 2020.06.rc2-py27.
• symlinks.json can be read from master branch, idk.

This proposal will solve at least the following problems of komodo:

• No more having to duplicate entries in repository.yml in order to keep the old versions
• Minimise danger of incorrectly copy-pasting earlier entries (libres in 2020.03)
• Proper diffs in pull-requests
• More organised git history

[markusdregi]

I think this is an interesting and sound idea :)