Added top level .jshintrc for global rules; removed corresponding JSHint directive

@juberti @marwahvikas @andresusanopinto PTAL.
Once you try to jshint on apps that split across multiple js files (such as test-rtc) wouldn't this list grow considerably?

Yeah I am in favor of strict.. just not sure about the global.
Regarding the remove the "use strict" I am not sure.. that string is used by the browsers so we could left it in.