Threading

The last to days have been spent on studying and implementing pthreads to our code. We need this to open a voice connection - while the rest of Pidgin keeps running.

Since it can be attempted to open several calls, or people can attempt to call you while in conversation, we must control the threading.
For now we have decided to spawn a maximum of 1 voice_client thread and 1 voice_server thread. That means we must make sure that we do not spawn to many threads, and that we notify where appropiate when a new call can not be done... (But what about calls on hold and conferencing... save that for later ;o) )

It seems to be working and synchronized using signals with the core of the plugin.