Copy DOM modules from purescript-angular

Basically unmodified (aside from removing redundant definitions) from https://github.com/purescript-contrib/purescript-angular/tree/master/src/DOM.  This way purescript-angular could use this package, so DOM bindings can be unified and worked on in one place.

I am not the original author, @ethul is, so I've also copied over his license, given that there wasn't one here already.