Feature/ffastrans improvements

[emcodem]

Sorry for sending all in one but you know how it is once you work on your own branch.. i'm still no git master unfortunately.

• HEVC should be straight forward, check the reversed uls on https://emcodem.github.io/smpte-ul-search/ ;)
• robust ama_path handling for Windows: not sure how you could live without this
• TransferCharacteristic: seems also pretty straight forward
• Descriptor linking robustness: should probably have sent in multiple pieces, it was important for me to forward existing locator
• do not clutter: not functional change but it felt a bit strange that all of this was just dumped to stdout originally, did i miss some way to turn that off?
• support forwarding unknown: it was important for me to forward unknown color metadata, not sure if this would break anything else but it feels right to do it this way
• prevent parse all klvs on non closed: very important addition, without this gigabytes of klv's are parsed if header is closedcomplete
• Prefers existing locator if the source mxf has one: as the title says... if the source mxf has the locator already, we forward it