inline nmea checksum calculator; use bootstrap style for button (#2180)
inline nmea checksum calculator; use bootstrap style for button (#2180)

* inline nmea checksum calculator; use bootstrap style for button
* also style 'Advanced' button and remove * and $, use text instead of html for result
* add a default string

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core