D0 initial sync

Added a new parameter/option for D0 devices: "wait_sync".
It's intended for devices that start continuously send data. For those devices (e.g. Hager EHZ361) the parsing of the messages at startup fails most of the times.
Currently only the mode "end" (so add "wait_sync" : "end", to the conf file) is supported which skips data from the device until the end of a message ("!") is found. This is only done once after startup and includes a sanity check to skip a maximum data to avoid an endless loop.