Implement sequence<DOMString> for keyPath ...

**Spec**: http://www.w3.org/TR/IndexedDB/#dfn-key-path

**Solves**:
https://github.com/axemclion/IndexedDBShim/issues/117
https://github.com/axemclion/IndexedDBShim/issues/105
https://github.com/MSOpenTech/cordova-plugin-indexedDB/issues/2

**Please Note**: Works For My Own Personal Use Cases &reg; :) Needs to be tested thoroughly to make sure it abides by the spec in the slightest bit