First DwC mapping

[peterdesmet]

This first DwC mapping consists of two files:

1. obis-to-dwc-mapping: Mapping the current Divebaord OBIS mapping to DwC, to at least get that data to DwC (data -> dwc)
2. dwc-mapping: A review of all DwC terms, to extend the current mapping to a complete DwC mapping (dwc -> data).

For both, a status column is used, with the following statuses:

1. keep/use: use or keep this term
2. n/a: term not applicable for these data
3. unnecessary: unnecessary term for these data
4. move: move current mapping to other term (= merging terms into one)

I also populated with example values I found, and corrected with stripe through where necessary.

Merge request if you agree with this approach. cc @DimEvil