Which files are downloadable could be improved

** Context **
Some files aren't marked downloadable when could be.

**Proposal and Constraints**
Change the "downloadable" field to mean
false - no
undefined - yes - use a default Download type by Upper Casing the format string
"xxx" - replace format with "xxx"
And for future use
function - apply function to file to get its downloadable string

**Success Metrics**
Not clear ... dont have a good example to test against