Webaccess fix

Massimo and/or Jano:

After the last commits I have been unable to compile (Unbuntu 12.04 64 bits, QT4) from the sources. I was getting the following error message:
```
webaccess.cpp:22:29: fatal error: QNetworkInterface: No such file or directory
compilation terminated.
make[1]: *** [webaccess.o] Error 1
make[1]: Leaving directory `/home/luis/qlcplus/webaccess'
make: *** [sub-webaccess-make_default-ordered] Error 2
```

After some searching on the web (and some trial and error) it seems to be that adding the line:
```
#include <QNetworkInterface>
```
to the *webaccess.cpp* file requires to add also the line
```
QT       += network
```
in the file *webaccess.pro*.to "add dependency to network module that provides QNetworkInterface"

As always check if this is correct, but after changing the file I've been able to compile without errors.

Cheers, 

Luis