Added option to disallow h1-3 tags

Closed
BO
7h ago
+1112-211

Hello,

this PR fixes issue https://github.com/panphora/overtype/issues/121 and allows users to disable h1-3 tags on a per-editor basis. Please note that I created this PR using AI as I'm not really a JS developer and am not overly familiar with overtypes code. I'm happy to adjust things if needed.

Cheers!