Check and validate scans

Most of the operators need the capability of excluding failed scans. During preparation or even acquistion, many scans may fail or be voluntarly aborted. Exclusion should be based on the capacity to reconstrcut the scan.

Common failures are: 1 - Num of projections are not matching the set amount of radiographs. 2 - Darks or flat not present

1 may easily be solved by getting tomo_n in /TOMO:.1/scan/technique/scan; if len(image_keys[image_keys=0])<tomo_n Then scan failed and if --raise-errors is enabled, should be excluded.