Feature: Add grid-style callout

- Adds `[!even_columns]` callout, an invisible callout which displays content nested within as a grid.
- Updated `MMW Design & Planning/Custom Formatting Features.md`.
- Deleted old `MMW_Faux-Grid_Callouts`.
- Deleted redundant `Obsidian-CSS-Snippets` folder as snippets are stored in `content/.obsidian/snippets`.

Author: MasssiveJuice08