Refactor: changes Features to Experiments

[JasonTheAdams]

What?

Closes #70

As per that Issue, this changes the concept of this having "Features" to instead having "Experiments".

Why?

It was agreed that it's clearer that the AI Experiments plugin contains "Experiments" for folks to play with rather than thinking it's introducing "Features".

Testing Instructions

Really just need to make sure nothing breaks. This doesn't introduce anything, just thoroughly changes the wording.

Test using WordPress Playground

The changes in this pull request can be previewed and tested using this WordPress Playground instance:

Click here to test this pull request.

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[JasonTheAdams]

I'm going to wait to merge this until after #67 is merged. I'll handle the gnarly merge conflict that will ensue, merge this, and call it a day. 😄