New feature - add cname rewriting in luci

DNSMASQ is supporting DNS rewitting , this work well .

But via luci , only a subset of feature are availiable .

This PR modify the web interface to add cname feature , can someone merge it ?

Seems like there are a lot of individual tabs already added for rarely used record types (hosts, SRV, MX, CNAME).. Maybe these all need to be combined into a common tab for these extra records.

Yeah, a simple dnsmasq raw config file block in LuCI would be nice. I add txt records manually for my various dhcp-reserved hosts (although that would probably be easy to add to the reservation config with a "description" field).

$ cat /tmp/dnsmasq.d/txt_records.conf
txt-record=panther,"Experimental RT3200 router, OpenWrt SNAPSHOT"