Switch JSLint to a submodule

When we went through switching JSLint from a core feature to a default extension, we removed the original submodule and directly uploaded the files. This reverts that by recreating the submodule at the commit of the current files we have.

This will allow us to easily update the version of JSLint later in the future. I haven't done it, since the latest version is checking for new stuff, like unused parameters, unused variables, don't use an else branch after a return, TODO comments, etc. giving warnings in almost every file. So, we would need to update the JSLint flags used on every file and fix other complains.

If we want to get the latest version, which would be good, so we have checks for more stuff (some of which are in JSHint and resolving issue #4462), I would suggest adding the `unparam: true` and `todo: true` tags and fix every other issue. `unparam: true` is required, since when using `triggerHandler` the callback receives as the first parameter the event, which is almost never used and makes JSLint complain. Making the modules with `define(function (require, exports, module) {` creates a similar issue, since we don't use all 3 parameters in each module.