`SecondsLeft` property is depreciated

https://github.com/ConvertAPI/convertapi-dotnet/issues/50

The `SecondsLeft `property of `/user` endpoint is deprecated. It's now replaced with two properties:

`ConversionsTotal`
`ConversionsConsumed`
    
Example

    "ConversionsTotal": 5000
    "ConversionsConsumed": 1642    