Gutenberg Support

[benlk]

Changes

• adds gutenblock, with settings options for:
  • [x] identifier (in main block in editor)
  • [x] lazyload
  • [x] sizes
  • [x] customClassName
  • [x] align
  • [x] alignwide
• slight changes to PR template to save keystrokes.

Why

For #70

Testing/Questions

Questions that need to be answered before merging:

• [x] does it work in 4.9.8?
• [x] does it work in 5.0-beta2?
• [x] do widgets still work?
• [x] does the widget accept the alignment properties?

Steps to test this PR:

1. Install plugin
2. Configure the plugin's breakpoints.
3. In a post, add a block!
4. Configure the block's sizes at its breakpoints
5. Configure the block's ad unit code
6. Set an alignment and check that that's respected.