Sort struct declarations in dependency order

[duck2]

Currently, structs are emitted in the order their corresponding complexTypes are found in the .xsd file.

Order them such that the root element occurs last and every complexType which is included in another type occurs before it(phew). This is required to declare structs as direct children of other structs. It also assists in viewing - just go up for a child type.

[duck2]

This works now.