[#4345] Remove extra DB calls in /project_iati_checks end-point
[#4345] Remove extra DB calls in /project_iati_checks end-point

This commit uses the prefetched IatiCheck objects to filter errors and
warnings, instead of making additional queries for them for each
project. This cuts down the time taken to populate the New IATI export
dialogue by 5-6 folds.

akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr