Keep only the newest value of single value properties

[blcham]

All datasets (e.g. time-analysis) should make sure that all "single value properties" (e.g. cm:age for aircraft) returns only one value.

A/C:

• model is changed to contain definitions of "single value properties"
• when we retrieve multiple values of "single value property" we should filter out older values (e.g. based on row number from input data)
• the pipeline has integrity checks to make sure we are providing and documenting the correct output