SPA_ID_* -> SPA_TYPE_*. We use 'type' for all registered types.
ID refers to either a registered type or an enum.
Improve introspection of object ids. Make 0 an invalid enum and
use it to look up the object id type.
Move some type-info files together.
Swap type and id of the object, we first specify the type and then
the id because the meaning of the id depends on the object type.
Pass client to some core functions to make it possible to check
permissions when iterating globals.
Check permissions of factory before using it.
Check permissions in link factory, only allow linking of nodes we can
see.
Check permissions in the autolink module, only try to link to nodes
we can see.
Make client permissions update behave like an atomic update of an
unordered set of permissions, which is perhaps a bit more intuitive.
