Now using MS_DEFAULT_MAX_PAYLOAD_SIZE . To change it afterwards using the
MSfactory in use, call  ms_factory_get_payload_max_size.

Audio filters update : replacing ms_filter_new/ ms_filter_new_from_desc by ms_factory_create_filter/ms_factory_create_filter_from_desc.
Fixing small issue in audio stream.c and text stream (Windows crash on audio_stream_stop and text_stream_stop).

avoid using CN with g722, it doesn't work because it's a wideband codec declared with 8000 Hz clockrate

 accessible from the MSFactory.
Adding MSWebCamManager* in MSFactory.
Adding MSFactory to MSWebCamManager* and pointer to manager in MSWebCam.
Using ms_factory_wbc_amanger or snd_manager get  to get pointers to the managers.
Using ms_factory_create to create a new factory and initialize it
(ticals ms_factory_new and ms_factory_init plugins and voip).

Add a define controling whether a rescaling of the signal should be done before entering in the G722 decoder

The new define is a private define and is called ENABLE_PCM_RESCALING. Its value can be 0 or 1.
By default, the PCM rescaling is disabled

Process ICE check lists in parallel (should prevent bug with pair that comes back to the waiting state when it might already be successful).

Using getter ms_factory_get_snd_manager to get MSSndCardManager from the MSFactory.
Using ms_snd_card_factory_get to get MSFactory from MSSndCard.
Removing static MSSndCardManager* scm.

.

Removing ms_factory_uninit_plugins when destroying the factory since it is already called in ms_factory_destroy.

Modifying ms_factory_destroy to destroy it and its contents when no one is using it anymore.
Modifying ms_factory_uninit to destroy the card manager and webcam manager when there is
 no  references to them.

This reverts commit 09acc3ca.

mediastreamer2-sound_card_tester still uses the fallback factory.
Added reference to MSFactory in MSSndCard an MSSndCardManager.

Since VAD/DTX capabilities are not signaled, the signaling of PLC capability is used as an approximation.

warning : fix TDODO in rfc3984_new .