Allow publishing of QTI zips in addition to perseus

[rtibbles]

Desired behavior

To support free response questions, we will be using QTI question rendering in Kolibri. To allow for this, if an assessment contains a free response question, we should publish the entire assessment as a QTI zip.

The best example to follow is Common Cartridge QTI package (CC QTI Package) linked here: https://www.imsglobal.org/spec/qti/v3p0/impl#h.9wxhfkbv60p0 - although the other sample packages may be illustrative.

Each outputted QTI file should contain a simple linear test with all of the questions as separate assessmentItems.

Sample XML for the choice (both single and multiple) and text entry (short free response) are available on the same page.

Current behavior

Currently all assessments are published as .perseus files.