Several changes and improvements

Made the install.sh script smarter in checking dependencies;
Added a STUN test request at startup, when enabled;
Added an option to specify the public IP of the machine, and fixed the information put in the c-lines accordingly;
Added an option to specify an RTP/RTCP port range (note: this depends on the availability of the related function in libnice, which apparently is not on my Fedora 18);
Made libopus and libogg dependencies optional (meaning the AudioBridge and/or VoiceMail plugins may not be built, if the libraries are not available);
Attempts to improve the FIR/PLI management in the VideoMCU plugin;
created utils.c file to contain helpers we may need in the future