Adding check for text headers in csv/tsv files

This is a quick fix for using csv/tsv files with string headers. The code checks wheather the first line in the file contains [a-zAZ], if so it skips the line, otherwise parses it like all other lines.

This should probably be fixed with a Java Pattern, or perhaps we could use a CSV library instead, e.g. Apache Commons CSV (https://commons.apache.org/proper/commons-csv/).