Decreased text persistence frequency to prevent history spam

[AlexW00]

Closes #3

preview at https://alexw00.github.io/notepadtab.com

[revolter]

Hmm, somehow, I didn't receive an email notification for this one, sorry!

I checked out your branch, and then:

• rebased it,
• fixed the conflicts,
• did some small refactorings, and
• added your "onblur" changes from #5.