Editor: use debounce instead of timeout

[shailendher]

Currently, the editor triggers an event on every keypress and this results in an multiple ajax calls and also bad user experience. (especially in the online editor)
lib.js:
form.on("input", "input, textarea", function() { form.trigger("change"); });
main.js:
form.on("change", function() { clearTimeout(timer); preview.addClass("loading"); timer = setTimeout(function() { var data = builder.getFormValues(); form.data("resume", data); postResume(data); }, 200); });

While there are probably many ways to optimize this, one option is to use _.debounce (lodash library is already part of lib) to rate limit the ajax requests.

I currently don't have vagrant setup but if there is enough interest I could make a pull request for this change.