TVB-2762: Fixed Complex numbers problem in Postgres

Created by: VinczeRobert

Postgres db has no datatype for complex numbers, it can only be achieved through defining a new datatype, which is a little more complicated, it requires some code in C as explained here https://www.postgresql.org/docs/9.4/xtypes.html.

So we thought with Paula that it would be easier just to have strings instead of complex numbers where there were errors (for Covariance and Complex Coherence Analyzers, the others didn't have this problem).