Add G'berg Block Transformation Helpers

[mikeselander]

Importing into Gutenberg blocks will be a common theme that we will see a lot of as we do more migrations into WordPress. Having a small library of helper functions that take in values and return block markup of a core type would make this importing process much easier and faster.

I'm envisioning adding support for core blocks that are used the most:

• Table
• Image
• Embeds (Instagram, YouTube, Facebook, etc.)