Fixed crashing parts.

* There were open file descriptors accumulating that caused a programme crash
  after a while. Not guaranteed to be safe now, but should be less likely to
  crash (at least it hasn't on my machine up to now ^^).
  It's these kinds of things that are not easily spotted by valgrind.
* CPU temperature information found in /sys/class kept moving around, so instead
  of taking a string from the config, I now read from an array of strings
  containing possible file locations instead.