Avoid segmentation fault when audiofile tries to unmap an audiolodec that is already unmapped

//TODO
Improve the ringtones quality

At startup, the installation directory is scanned and the available shared library
(codecs) are loaded in memory.

The previous commit brought a segmentation fault when launching the client.
When the daemon is lauched separatly, it uses a wrapper script, but it doesn't when the client start the daemon.
SO the LD_LIBRARY_PATH was ignored and the daemon couldn't find the dynamic library for the codecs.

Codecs dynamic libraries are created at the compilation time if they don't exist and copied in /usr/lib/sflphone/codecs at the installation

Note: Manually copy the .so library in /usr/lib , then ldconfig

Tiny doc fixes and typos.

Adding magnetism to dtmf window
Adding sample rate combobox

Samplerate is now a dependancy.

Add audiofile for playing wave on incoming call

Add a new audiofile module