[Improvement] Changing DIO polarity terms

[Snapyou2]

Good morning,

As the DIO channel polarity dropdown description is not very explicit in the Post Processing tab, I would suggest using "Start of event 0 → 1" or "Start of event 1 → 0" to make it more clear, since "Event high" or "low" can be hard to understand.

Thanks and have a nice day!