ATM we only support 'quantity' data types in SDoC for statement **qualifiers** AND when entering data for a qualifier whose property has a data type of "quantity", the user can't enter units for the quantity, only a number
In wikidata the user can enter the number and the units - e.g. if the statement is 'length' they can add the value for length plus 'metres', 'inches', etc
We want to support top-level statements with quantity data types, plus units for those quantity values, so we can have statements about, for example, the dimensions of an image
##Examples
A quantity can be population, maximum capacity, floors above ground, and numeric value, or others (see full list of Wikidata properties that use the quantity data type).
##User story
As a Commons editor, I want to add a quantity to a media file’s metadata, so that anyone using that file can know a particular kind of quantity pertaining to that file, including the unit of that quantity (optional).
##Acceptance criteria:
[] can enter statements with quantity values as top-level statements, not just qualifiers
[] can enter units for the quantity values
[] via File page
[] via UploadWizard