Chain - json: add a table containing attribute name and data type, about each entity in chain

[laurivesa]

this can be one table with four columns: entity (name), attribute (name), data_type (as in Arena), and category/taxon table name.

The 1st reason is that in R these all are as characters: text, categorical, taxon. In data analysis, it is beneficial to know what are categorical & taxon attributes.

The 2nd reason is that in R, for example entity 'tree', is actually a view from DB, and we do not know which attributes belong to entity, and which to its parents.