Port the survey analysis code to work on the database content

[fjankowsk]

The survey analysis code currently works on the MeerKAT sensor data, which are pulled in externally at irregular intervals.

It would be great if someone could port it to work on the contents of the candidate database. This would provide a slightly more accurate survey completeness analysis and allow other studies in the future. Care should be taken to merge the code in the sensor dump analysis with the one that already exists for the database entries.

This should be reasonably easy, but it requires some care and testing to be done correctly.