Adding spell checking support

[anisus]

The game is currently using CodeMirror for the editor. Unfortunately, that means it cannot use the built in spellchecker of the browsers. And we want spell checking.

One solution is to add typo.js with CodeMirror, as described here:
http://stackoverflow.com/questions/12343922/codemirror-with-spell-checker/12462720#12462720

However, the dictionary file is close to 12MB, but will be almost 1MB when sent over the network using gzip.

Questions:

• Is it worth the extra download?
• Should it be configurable in the settings (set cfg spellcheck = on)?
• Should it be on by default?