cshark-luci: remove 'certificate' from web interface

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
luci-cshark: add capture by 'seconds, bytes or packets'

Also put it in a table and do some minor changes.

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>