#3957 added string file parameter to getStrings request.
Issue #3957 Refactored getStrings method for ios.js and ios-controller.js. cb is now last method parameter. Also update Android and Selendroid getStrings methods with stringFile parameter to fit getStrings method parameter called in controller.js. Added test for method parseLocalizableStrings in ios.js.
Issue #3957 changed undefined to null in ios-device-specs.js and corrected parameter of call of parseLocalizableStrings function in ios-contoller.js