mpegtsmux: Add support for aggregating multiple ES packets for one PES packet

Submitted by Sebastian Dröge @slomo

Link to original bug (#757567)

Description

See summary, this is especially useful for audio where packets are usually very small and we can otherwise easily get 100% or more overhead caused by the PES/MPEG-TS packetization.

ffmpeg does this for audio, and has a parameter to configure how much at most should be aggregated per PES packet