CapellaMBSE doesn't add necessary namespaces

[Wuestengecko]

When creating objects from a new namespace (i.e. one that isn't already registered in the model), the namespace must be registered as xmlns:... on the root <Project> element. Not doing so results in a broken model which cannot be loaded in Capella, until either the namespace is registered or the offending element(s) removed.

In the same way, when removing the last element from a certain namespace, that namespace must be unregistered.