Check for consistency of server responses

[KumbuT]

Server responses are not consistent. The designed response was to have the format:
{
"success": true,
"message":
}

However this doesn't work well if we're sending data over "message" JSON attribute because the caller has to check whether they got a JSON object or a String in the message.

I propose that we change the format to:
{
"success": true,
"message": ,
"data":

}