libtorc-core: Add another javascript translated string
libtorc-core: Use a variant map for property change values in
TorcWebSocket

- this simplifies the javascript code at the other end and makes the
return consistent with the value property of an initial service
subscription response.
libtorc-core: Add TorcCoreUtils::GZipCompress and
TorcCoreUtils::GZipCompressFile
libtorc-core: Support gzip compression in TorcHTTPRequest
libtorc-core: Use gzip compression for some content.
libtorc-core: Use gzip compression for http service responses.