ats_speed: PageSpeed optimization plugin

Pull in the plugin code from https://github.com/We-Amp/ats_speed.
This adds the plugin as-is, and doesn't wire up to automake yet.

As this plugin needs to download external libraries to
build, a custom make file is added.

See README.md for setting this up.

For more information see
https://developers.google.com/speed/pagespeed/optimization and
http://www.atsspeed.com/

Plugin is donated by We-Amp, ip cleared via:
http://incubator.apache.org/ip-clearance/ats-ats_speed.html
Jira ticket: https://issues.apache.org/jira/browse/TS-2926