htpdate: modify init scripts to use procd and uci configuration

htpdate: modify init scripts to use procd and uci configuration

Modify init script to use standard uci configuration and procd for
process management. We benefit from:
- use of standard LEDE configuration with its ability to revert and
  commit changes
- validation of configuration variables
- procd taking care of restarting daemon when config changes and user
  wants to reload it
- automatic respawning of daemon process in case it dies

The source is patched to make it possible to run as a daemon in
foreground.

Signed-off-by: Marcin Jurkowski <marcin1j@gmail.com>