include more trait datasets incl. Std version

[fdschneider]

the package should provide more datasets from the living spreadshet (https://github.com/fdschneider/bexis_traits/issues/20).

• [x] identify data for integration
• [x] write script to extract data upon call of data() (files are placed in 'data/' directory)
• [x] include documnetation in package files 'R/data.R'

A standardised version of each dataset should be provided as well (linking to trait Thesauri and taxon Ontologies).