input.Makefile: $(tables): Allow datasource to specify custom import order in src/import_order.txt

mappings/Veg+.terms.csv: growthForm: Documented source of standard terms

inputs/SALVIAS*/src/1.organisms/map.csv: Removed no longer applicable comments, which related to mappings that were in effect long ago

inputs/SALVIAS/src/2.stems/map.csv: Added comments from corresponding SALVIAS-CSV organisms columns

inputs/SALVIAS*/src/1.organisms/map.csv: Habit: Mapped to new Veg+ habit term

inputs/SALVIAS*/src/1.organisms/map.csv: Habit: Don't filter out values not part of the provided terms list, because such values should be flagged as invalid in the error maps rather than silently discarded. This also ensures that any valid values which are not part of the provided terms list are kept.

mappings/Veg+-VegCore.csv: habit: Map to new verbatimGrowthForm since this field is not necessarily standardized

mappings/Makefile: Veg+.cs-VegBIEN.csv: Join new Veg+-VegCore.to_self.csv (self-join), instead of Veg+-VegCore.csv, to VegCore-VegBIEN.csv, to support two-level chains of mappings in Veg+-VegCore.csv

mappings/Veg+-VegCore.csv: /_alt pass through mappings: Removed comment because the two-level mapping propagates it to all fields ending in /_alt, even though it doesn't apply to them, causing the main VegBIEN map and several datasources' maps to change unnecessarily. Also, the comment is not completely accurate because /_alt pass throughs are now used primarily to support idempotent self-joins of Veg+-VegCore.csv.

union: Don't eliminate duplicate rows based on matches between map_0's output column and map_1's input column, because union is now being used for self-joins and it is legitimate for a term to appear as both an input and an output