Offer an implicit PortNumber from ScalaTest + Play traits that provide server

-Added PortNumber and WsScalaTestClient
-Added implicit port number to AllBrowsersPerSharedTest, ConfiguredBrowser, ConfiguredServer, OneBrowserPerSuite, OneBrowserPerTest, OneServerPerSuite and OneServerPerTest, 
-Mix WsScalaTestClient into PlaySpec and MixedPlaySpec.