Unify qml and normal client more.

I would suggest dropping the qml parser status.
Make apiUrl a property of EnginioClient.

There is no point in duplicating this in the
qml version of the client. QML handles QUrl just fine.
The following works just fine:
    Enginio {
        apiUrl: "https://api.engin.io"
    }
Move sessionToken property to EnginioClient

This leaves the EnginioQmlClient basically empty.
Ideally the normal EnginioClient can simply be exposed
to qml.
Merge pull request #18 from gladhorn/initialized-state

Unitfy the two client classes to have less duplicate code.