flow granularity

This is a proposal to document that intents, commitments, and economic events can be used in VF for any level of granularity. This means that for analytical or higher level planning, budgeting, etc., we can use the same flow classes as for operational needs.

If using as higher level flows, it could be possible that there are lower level flows that roll up into the higher level flows. I'm not including any data structures to express that, thinking that can be inferred from the situations and if needed, from the dates, resource classifications, etc.

To make this happen, I changed the date/time related properties to use time:TemporalEntity, which is subclassed into Instant and Interval, per this spec https://www.w3.org/TR/owl-time/#time:Duration. This was originally suggested by @bhaugen in this issue: https://github.com/valueflows/valueflows/issues/152. The dates/durations of events and commitments needed to be cleaned up anyhow, vf:start was not working in practice. I assume that specifying the superclass infers that people can use any subclass - please confirm @elf-pavlik .