Add 'Read' instances for most objects

This allows a cluster structure to be easily serialized via "read";
together with the already existing instances of Show, this gives a
poor man's serialization/deserialization implementation.

The patch also exports the compDetailedCV function from Cluster.hs, so
that it can be used by other modules too.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Balazs Lecz <leczb@google.com>