Extract proof-of-concept code and demo material into a separate repository

[emetsger]

As the API-X codebase matures, it becomes more difficult to manage the proof-of-concept related material from the core code. Not only can it be more difficult to manage, but it also doesn't make sense to keep mature code together with code that is intended to demonstrate nascent concepts. Down the road, it may make sense to promote the API-X code from the "labs" repository, but leave the proofs-of-concept behind.

Ideally, the proof-of-concept (POC) related items can be separated into a distinct repository, for the reasons discussed above. The POC repository should maintain its history from this repository.

[emetsger]

The refactor-poc branch in my fork contains the proposed git history and file structure for a new repository dedicated to the proof of concepts. The contents and history of this branch would be pushed to a new repository under fcrepo4-labs.

git filter-branch was used to select the history of the proof-of-concept related material, including the docker and proof-of-concept subdirectories, as well as various readme files and POMs. POMs were subsequently edited to build the code as appropriate.

[emetsger]

Note that multiple invocations of git filter-branch were used and later merged into the refactor-poc branch. It may be possible to string together all of the various filters into a single invocation of git filter-branch and remove the merge commits.