Read temperatures from system files and list IPs of all active broadcasting interfaces. 

monitor.php
=========
Current and limit temperature read from system files instead of from vcgencmd utility.

- The utility vcgencmd is not preinstalled in all distributions, especially not
  in minimalistic ones. It is recommended to read temperatures from system files:
  - Current temp: /sys/class/thermal/thermal_zone0/temp
  - Limit temp: /sys/class/thermal/thermal_zone0/trip_point_0_temp
- The reading of the limit temperature has been included for future use. Is is
  the maximal allowed temperature for Raspberry Pi. Usually, at reaching this
  value the system is forced to shutdown.
- The naming of temperature variables has been unified.

lib/function.php
===========
IP address list of all active and broadcasting interfaces.
- The Raspberry Pi can be connected to LAN concurently with
  more interfaces, e.g., with ethernet (eth0) and WiFi (wlan0).
- The function getServerAddress returns sorted list of all IPs,
  so that it needs no input argument anymore.
- If there is no active broadcasting interface available,
  the IP address reads "n.a." clearly indicating this fact.