Support dynamic package bootstrapping

The parent window of a Montage application that specifies `data-remote-trigger` in its `montage.js` `script` line can now inject a package location and dynamically generated `package.json` into the child application.

The child window sends a `montageReady` message to the parent.

The parent may then send a `montageInit` message to the child, with an optional payload. The payload may include a package `location` or `packageDescription`.

This includes a demo.