A better spellcheck

**Is your feature request related to a problem? Please describe.**
The spellcheck is pretty bad... And the [library used[(https://github.com/sparksuite/codemirror-spell-checker) hasn't been updated in 4 years.

It is aggressive in highlighting words as being typed, thinks numbers are spelled incorrectly, and doesn't allow us to specify our own (additional) dictionaries.

**Describe the solution you'd like**
pipe dream: Native spellcheck with both textarea and contenteditable
pragmatic: something like [Codemirror-Typo](https://github.com/pirtleshell/codemirror-typo) or [this slightly updated Codemirror-Spell-Check](https://github.com/edemaine/codemirror-spell-checker) and allowing us to include our own dictionary files
Maybe even https://github.com/wooorm/nspell

**Describe alternatives you've considered**
I just disable it... which is bad in a different way.

**Additional context**
not really applicable here.