[#109] Update version attributes to be of type xsd:string

This is more appropriate now as they are checked against a codelist, and
we want to be explicit that 2.01 and 2.010 are NOT equivalent.
Change type of linked data attributes to xsd:anyURI
Implement description changes from Bill's spreadsheet

https://docs.google.com/spreadsheets/d/1yXBgKrntAPbH6GTmH3ay-32OCuId8p9gvqGHxjRrYmk/
Move iati-identifier out of common schema

(now it's redefined in activity schema)
budget-line
update organisation standard wording