Added unit test for Logger (based on OCLoggerUnitTests.m)
Added unit test for Logger (based on OCLoggerUnitTests.m)

ibm-bluemix-mobile-services/bms-clientsdk-swift-core,ibm-bluemix-mobile-services/bms-clientsdk-swift-core,ibm-bluemix-mobile-services/bms-clientsdk-swift-core