[WIP] Chosen version that doesn't rely on JS library

As per #1380, this is an in-progress implementation of Chosen that does not rely on any specific JavaScript framework, and hence can be used in any scenario.  It is currently unfinished and has some minor bugs around reopening of lists, but I felt it was worth getting a code review and feedback from the official developers at this point (as well as code contributions!).

At some point in the future, the jQuery version could be a small adapters over the top of this "native" version, just "plugging the holes" (by overriding internal methods and replacing native implementations with jQuery implementations), and providing a jQuery-friendly API to consume. This would significantly reduce the amount of code duplication.

To do: 
- [ ] Fix IE 8 (it's so close.. The multi selects work, but the regular select doesn't!). Note that the custom events do not work in IE 8 due to browser limitations. This can be worked around, but I've deemed this a low priority since jQuery/Prototype can be used to get IE 8 compatibility
- [ ] Rename index.html to index.jquery.html and index.native.html to index.html
- [ ] Test on mobile browsers
- [ ] Unit tests for helper methods (see https://github.com/Daniel15/JSFramework/tree/master/tests for example)