More dialog boxes

[owlang]

Add dialog box when running into errors during file loading (e.g. incorrect header "YORF" instead of "NAME") OR if data loaded is empty or length=0

[owlang]

Another edge case: file contains "sense" or "anti" row but does not contain the other - expected behavior is to fill other strand with zeros and pop-up a warning to the user that the other strand is empty