kmsaudiomixer: Use liveadder instead of an adder
kmsaudiomixer: Use liveadder instead of an adder

live adder mixes audio according the their timestamps and waits for some
milli-seconds before trying doing the mixing. Because this element
does not propagate EOS signal on its src pad, we have also removed
probe, so we will lose data in buffer are queued in live adder element

Change-Id: I94e7e86193d195d18f9e7d966240e178c66c855c

shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,Kurento/kms-core,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,ESTOS/kms-core,TribeMedia/kms-core,ESTOS/kms-core,Kurento/kms-core,shelsonjava/kms-core,ESTOS/kms-core,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins,TribeMedia/kms-core,ESTOS/kms-core,shelsonjava/kms-core,Kurento/kms-core,TribeMedia/kms-core,Kurento/kms-core,TribeMedia/kms-core