Implement flag toggle

[slifty]

There is a toggle button that allows the user to trigger whether or not the language checker is active. The logic powering it is that if a user just starts typing, the toggle must be manually set. However, if the user copies a bunch of text into the empty text box the toggle will automatically activate.

When active, language gets checked every time a word is modified in the text area / the language checker interfaces / highlights are enabled.