XSD: change `xs:sequence` to `xs:all`

The XSD currently uses xs:sequence to define attributes of types. This requires the children of elements in XML documents to be in the exact same order as defined in the XSD, which results in the unnecessary work of re-ordering code-blocks in serialization adapters, as seen in !67. Changing xs:sequence to xs:all would remove this limitation, allowing children in any order to be valid against the schema.

On the other hand I could see why you would want a certain order of elements. For example when manually inspecting XML documents (which can get quite large), a fixed order of elements would make objects easier to grasp. But then again, you would most likely use XPath or good XML viewers to view such documents anyways.

What's your opinion on this?

forwarded to DotAAS-Group: Issue 20