Modal

# Changes

 - If modal has a `.js-modal-close` link, also allow user to close modal by clicking overlay. Closes DoSomething/dosomething#1128.
 - Exposes public API for modals: `NEUE.Modal.open($el, animated)`, `NEUE.Modal.close(animated)`, and `NEUE.Modal.isOpen()`.
 - Adds modal hash to location bar when opening a modal. If there is a hash for a valid modal in the URL on page load, open that modal automatically. Closes DoSomething/dosomething#1843.