libav muxer: added WEBM support
descrambler: fix TSS_NO_ACCESS reset for buffered packets
remove pkt_merge_header()

- rename pkt_header to pkt_meta
- unify logic for the metadata processing
- add meta field to components to the htsp stream start message
htsp: log subsystem should be lowercase
transcoding: simplify streaming_start_t structure copy
Merge branch 'master' of https://github.com/tvheadend/tvheadend