Added the typesafe config to read default config values

Added the library typesafe config to read default config values. The order followed is system properties, asynchttpclient.properties and then defaultahc.properties. defaultahc.properties has all the default values for each of the configuration properties and these could either be overridden by a system property or asynchttpclient.properties
I think testing this is not very useful: it's actually testing the config library.