Proxy support

Server-side requests for google places data will sometimes come through
a hosted cloud provider where outbound TCP requests are sent through
different IP ranges. Since Google has IP white listing there is a need
to have a static address for these requests. Using a proxy is the
typical solution to this.

I've added support for specifying a proxy parameter which simply calls
the node request library (and I've implictly added a dependency on the
request library).