Reorganize abstracts & interfaces

[borkweb]

• Reorganized abstract classes and interfaces into Contracts/ directories. (I like that approach from Give)
• Switched away from StellarWP\Schema\Container in favor of using lucatume\DI52\App and lucatume\DI52\Container.

This builds on top of #5 with the intent of being part of 1.1.0.

Addresses: #8 and #9

[JasonTheAdams]

@borkweb Rather than introducing a new package and container in multiple packages, I'm inclined to make it possible within package configuration for the implementing plugin to provide its own PSR-11 compatible service container instance — which is then used by the package. What do you think?

[JasonTheAdams]

Man, that PSR-11 interface sucks more than I realized. It's way too limited. It doesn't even have the ability to set items within the container, much less singletons. We may consider making our own StellarWP/Container package that's, at the very least, our own interface.

[borkweb]

@JasonTheAdams - I agree that it'd be great to provide a way to inject a container. That being said, I'd love this library to provide a sensible default for those that do not have the desire or knowledge of how to provide a container. We definitely need to have a more lengthy conversation around this topic with some more folks.

[JasonTheAdams]

I guess that depends on the assumptions we're willing to make. If we include this as a default for every package that uses a Container, then that's increasing the size of that package (and plugin) by ~1 MB/plugin — assuming this PR gets merged and it's not 50 MB: lucatume/di52#39 😬

At this point, I'd be willing to assume the implementing plugin will provide its own Container to reduce size and complexity per package, until such a time as folks complain and make an Issue. Even then I'd still prefer to have a separate Container package we can point folks towards to implement and provide.

[borkweb]

Switching this back to draft mode because #14 rethinks some of the foundational elements that these changes build on.

[borkweb]

Alrighty, with the addition of a Config class for Container and DB objects, this PR is now solely about relocating the interfaces and abstracts.