streamlineGlobalContext: Support resetting global context before handling request

In streamline, the global context will persist unless you reset it at the beginning of the request. This PR wraps the app.handle method to reset the context before continuing processing the request.

Edit by @aseemk: fixes #12.
Actually maybe `value` is a better name, also for the query string then. `GET /global?value=foo`. (And easy enough to just use the passed-in value then. So it'd return `{value: 'foo'}`.