alarm/fake-hwclock: use systemd timer unit, to 0.3

* PKGBUILD: modified to install directories with correct permissions (in
  case of a restrictive umask).
* PKGBUILD: change arch to any as this is arch-indep.
* fake-hwclock.sh: add 'load' command that sets the system time only if
  the current time is older; make 'set' an deprecated alias of it.
* Add fake-hwclock-save timer and service that saves the time every 15
  minutes.
* install: suggest to enable timer unit instead of cron.