JVET-Z0072: enhanced referencing configs for random access and low delay

Without this fix, the "performance" low delay configuration file yields
worse R-D performance than the "regular" low delay configuration

Shorten parameter names to NNPFC to save space in user manual (an maybe make them easier to type).

No specific table formatting is required for NNPFC anymore.

- Add the control for that flag in the cfg file & update the manual doc
- Implement checking at encoder side to ensure that when sending an update the base filter is already present
- Implement detection at decoder whether the given base filter is a new or a repetition filter.
- Implement checking at decoder side to ensure that when receiving an update filter, the base filter has been received earlier / already present.

prefix byte