switched to holobranch: emergence/legacy

The template site now pulls its code entirely from the emergence/legacy branch that is published via hologit from the emergence-legacy holobranch

This means that 3rd-party libraries are now merged in directly from their source repositories each time the holobranch is projected, rather than the legacy process for sources relying on php-config/Git.config.d/*.php being initialized as sources within a site instance and then manually merged into the develop branch.

Gradually, all 3rd-party code and php-config/Git.config.d/* files will be deleted from the develop branch and instead represented via holosource configs in .holo/sources/ and mapping configs in .holo/branches/emergence-legacy/

Any sites inheriting from or will immediately see a wave of minor updates to 3rd party libraries, and going forward will see minor- and patch-level updates to 3rd party libraries coming down shortly after their release.