travelmate: release 2.3.0-1

travelmate: release 2.3.0-1

* split travelmate.s in a new central travelmate function library (usr/lib/travelmate-functions.sh) plus
  a smal service script (/usr/bin/travelmate-service.sh)
* the vpn-, mail- and login scripts are now using the central function library
* rework the ntp hotplug script
* harden the config parsing
* support the curl interface option to specify which network pathway is used for outgoing requests
* the travelmate status now includes the backend- and frontend version information
* LuCI: use a special travelmate interface, e.g. trm_wwan or use an existing wwan interface
* LuCI: no longer call the logread binary, use rpc / the ubus log object instead
* LuCI: various code cleanups
* LuCI: various small usability improvements
* readme update

Signed-off-by: Dirk Brenken <redacted>