…Sections

This indirection isn't really necessary now that its use in the high level rest client went away.
-> flattened the `SearchResponse` class to make ref counting easier
-> removed `InternalSearchResponse` whose functionality was completely redundant now
-> removed serialization and most of the usage of `SearchResponseSections`, only keeping this for
the few search execution spots that currently use it and where removing it won't get us anything and
will be a huge changeset.

…earch-response