Pipeline-csv

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+ Method csvfile.last_weld renamed to csvfile.last_pipe and returns pseudo pipe without length, that starting from last weld.

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- Fixed error on reversing object with custom data set.

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- Fixed possible KeyError in `summary_text` function.

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+ Custom data moved from field `04 ObjectName` to `17 DistMR` (for all object classes).

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* Remove Python 3.7 support.

+ New ObjectClass.DIAM item for pipeline diameter changes.

+ Custom data for ObjectClass.DEFEKT and ObjectClass.MARKER.

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+ Method csvfile.last_weld returns data row for last weld.