Add a fake dereferencing item '*' to CDB for dumping QString*, etc.

Simplify the symbol group recursion to oblivion and make
it parametrizable with predicates to control recursion and
further processing. Most importantly, insert a parent item
BEFORE its child item (ignoring for now the fact that child recursion
might fail), making it possible to check and do magic on the parent,
disabling further handling by the symbol context. Dumper handling
can then kick in and handle pointed-to dumpeable items by inserting
fake dereferencing items.
Remove logic to detect already expanded items, just re-insert the
children if the handler asks for it.