Feature fix/whitespace confidence

[chaddy314]

This Pull Request adds the ability to handle whitespaces (U+0020) in Textviewer confidence view:

• Each whitespace will be represented as ⌴ only when it has been flagged above or below the tresholds.
• Copying the character to clipboard will of course copy the true whitespace (U+0020) character and not its replacement (⌴).
• Blank Words and Glyphs are now represented by 🞍 (Black Slightly Small Square; U+1F78D).
• A timeout has been added to the threshold inputs to inhibit calculating the ouput on every increment.