Addresses #48. CT xlsx export now works with patient age criteria. Also improved filtering to only filter on fields that have a value. This would probably have been a better way to fix previous export errors - see #28 and #43. TODO apply new technique to csv CT, fluoro and mammo exports -- see #49 -- and add age filters to fluoro and mammo.
Fixes #48 and #49. Patient age filtering and exporting now works. Exports are now more robust rendering the modifications made for refs #28 and #43 unnecessary. Filtering before exporting is now unnecessary - see #50 for docs changes required.