Changes as made by @Luuk. It would be good to remember why I made all the numbers into strings in the first place! Needs further review and testing. Changes should be made to all xlsx exports accordingly. Refs #443
Set date format for dx xlsx from settings. Now using xlrd to test value types and values. Pandas too keen to convert to numbers so testing ineffective! Fails against patient ID as currently number. Refs #443. Need to redo tests for CT with xlrd.