Replace own filewatcher with chokidar

[tonistiigi]

Currently Styler uses it own custom file watcher wrapper. It kind of works but I've experienced Styler crashing when I do git checkout or git reset for the project. Anyway, we shouldn't deal with these things and should use chokidar module instead.

Note that chokidar doesn't support many listeners to a single file without reaching maxListeners limit. So this needs to be added to either chokidar or Styler.