Sorting for attributes on save

As QHash is used, attributes come out in a random order. This easily causes other software handle files as text, such as versioning systems, see them as changed.

Now this can be worked around with qSetGlobalQHashSeed or QT_HASH_SEED, but that is global setting.

Instead a simple alternate save() function or a property to tell if it should save in the same way. Probably easiest would be to simply sort all attributes by their name before writing them.