Improve text definition of `gist:sequence` and consider renaming

[dylan-sa]

The current definition of gist:sequence is "For ordering ordered lists," which is more about how the predicate is typically used than a definition.

Additionally: To my knowledge "sequence" ordinarily refers to a collection of things that are sequenced (as in a sequence of events or numbers). For this reason, I wonder if a name like sequenceNumber or sequencePosition would be more appropriate.

Proposal:

1. Update text definition to indicate meaning: "A number that specifies the position of an element within an ordered collection or sequence."
2. Move current definition to a skos:scopeNote.
3. Revise predicate name along the lines suggested above.

[rjyounes]

I prefer the simplicity of sequence. I agree that the definition needs to be updated.