Update to loggly-csharp library

Added few more fields like applicationName, userAgent as a part of the library to easily identify the application and the type of library used to send logs to Loggly. Set "userAgent" as "loggly-csharp". Application Name is optional. Its default value will be "loggly-csharp-app". Added one more constructor in order to not to force users to pass null as a value if they want to pass "applicationName". Fully backward compatible. Also updated the default value of the URL