Move debugger plugins into separate qml1tooling directory

Separate the QML 1 and QML 2 debugger plugins. This helps avoid
a nasty crash in libgobject when (uneccessarily) loading and unloading
the wrong plugins.

Task-number: QTCREATORBUG-9232
Change-Id: I0bce7b364fcce983ccaa531d9008609ff08bb77f
Reviewed-by: Aurindam Jana <aurindam.jana@digia.com>