Add virtual collection RAS_TYPES

[Dimitar Misev]

.. as a shortcut for getting all types with one query. Currently we need to fire 3 separate queries for cell, array, and set types.

It should be implemented in mddcoll.cc to just return a union of struct/mdd/set types, what you currently get with these 3 queries:

rasql -q 'select c from RAS_STRUCT_TYPES as c' --out string
rasql -q 'select c from RAS_MARRAY_TYPES as c' --out string
rasql -q 'select c from RAS_SET_TYPES as c' --out string

at once with this query:

rasql -q 'select c from RAS_TYPES as c' --out string