LPS-33812 Add Liferay spellchecker to ckeditor

Hey Byran, 

Can you help me review the code for the spellchecker? This is the one without ads.

liferay.spellchecker.js contains the code for the actual spellchecker
aui-replacetext.js contains the code that replaces the DOM text is from here: https://github.com/padolsey/findAndReplaceDOMText with some modifications to it

I wasn't too sure if I needed to rewrite the code in aui-replacetext.js since it is using regular javascript.

Let me know if you have any questions.

Thanks