Extend dns plugin

This adds the functionality to add TXT records to etter.dns.
In addition TXT and ANY queries are answered.
At the moment responses to ANY queries contain corresponding A,AAAA and TXT records.
This is in the function parse_line, so parsing the current line will be stopped and a return value of 1 means that parsing was succesful, meaning that the result will be added to the List of dns_spoof_entry.