Add `close-on-click` and `close-on-escape` options

I wanted to use `ic-modal` to do confirmation dialogs in my app and closing the modal without using the actual buttons wasn’t working, so I added options to configure it. The default is still to close when clicking the overlay or pressing escape.

PS. I also fixed the build to be able to do this PR, tell me if you ever merge https://github.com/instructure/ic-modal/pull/12 so I can rebase master.