Rough draft of patternception POC

[johnstonphilip]

This branch is a POC of how patterns-inside-patterns could work:

How to test

1. Whenever you want to use a pattern inside another pattern, use the PM:Pattern block:

2. Type the name of the pattern you wish to use (this should instead be a list of patterns in the theme to choose from)

3. When you save the pattern, the block code saved to the file will use the

4. When you load up that pattern again, it will be using the PM block.

To do:

• Make the "Edit This Pattern" button save the current pattern, then open the pattern in question.

- Possibly, make our pattern block show a preview of the blocks inside that pattern (but they should **NOT be editable**)

[johnstonphilip]

To match core, the value saved to the slug attribute would have to match the registered slug for the pattern.

[johnstonphilip]

Note: The reason we can't just use core's pattern block is because upon save, it inserts the pattern, wiping out any use of the core pattern block.

[kienstra]

Hi @mike-day and @mikemcalister,
Is it alright to merge this PR?

Patternception is a work in progress, but we can always deactivate it by removing a few lines of code.