idnode prop: added support for str_enum

This allows classes to define enumerated types, such as required for the
DVB FE configuration.
mpegts: add full DVB mux configuration support

I have still not added ATSC (lazy) but C/T/S are all added. There is no
attempt to base the options on the hardware support, user is expected
to know anyway. The AUTO options could possibly be checked, but my guess
is that these days most tuners support AUTO modes anyway.
webui: added support for enumerated types in the editor panel
mpegts: start adding routines for creation of muxes from UI

This includes a new routine that operates using a full htsmsg_t config
rather than dvb_mux_conf (used for auto-detection).
webui: can now create new muxes from the UI

This needs testing and I'm sure some data validation would be useful!
webui: some fixes to allow proper creation of networks and muxes