watchcat: add nopingtime option + refactoring

nopingtime UCI option rationale:
I want relatively fast reaction(i.e. 1m or 2m) for 'no internet' condition,
but i don't want my router to reboot every 1 minute if there is still no
internet after reboot.

initd_watchcat:
* add: nopingtime uci option support
* add: defaults to all non-critical options
* add: log warnings for non-critical errors(when option is missed and
default is applyed)
* fix: error handling and config_get defaults are somtimes in conflict
because of config_get defaults. They are gone now, error handling improved.
* fix: calling watchcat.sh with 'period' mode instead of 'ping'. Typo?
* fix: pingperiod default changed from period/20 to more reasonable period/5

watchcat.sh:
* add: nopingtime uci option support( sleep if uptime < nopingtime )
* remove: [ "$mode" = "allways" ] && mode="always" - not needed, already
done by initd_watchcat in load_watchcat() func
* add: echo 1 > /proc/sys/kernel/sysrq before sysrq-trigger
* refactor: eliminated once used not needed variables, code size reduced.

* PKG_RELEASE bumped up

Signed-off-by: Vasily Trotzky <trotzky.vas@gmail.com>