Use Q_PROPERTY for backendId and backendSecret

The properties should be visible in qml.
Say hello to EnginioReply.
Say hello to Enginio::Areas.
Add QJSON based api to EnginioClient.

The change allows to use QJsonObject for enginio queries.
Say hello to EnginioModel

EnginioModel is a class that transform a json array to a Qt model.
Expose new enginio interface to qml
Register basic Enginio types in metatype system.
Add json api tests
Simplify debugging by always including QDebug