QmlDesigner: Support for enums in alias properties

Also the qmlpuppet could not handle enums in combination
with alias properties. Enums on alias properties are handled as
bindings. This is just an intermediate solution until we refactor
the handling of enums in the model.

Do not integrate this patch to 3.0 or master.

Task-number: QTCREATORBUG-10114
Change-Id: I022637285deb5ff13b61d761d89b3ae1201575db
Reviewed-by: Marco Bubke <marco.bubke@digia.com>