accesslib: make_context_subobj() now expects ctxlevel, and fix all callers

accesslib: make_context_subobj() now expects ctxlevel, and fix all callers

make_context_subobj() was not providing a contextlevel property, and
no callers fetched the field. This comes from its humble origins where
it was only ever called for course objects. These days it's used in
many other situations, so this patch DTRT and

 - fixes make_context_subobj() expect a cxtlevel and turn it into
   contextlevel

 - fixes all callers (accesslib, datalib) to provide it