Allow Exemplar to be to another CFitem

[brandonopened]

As an OpenSALT editor I want to be able to use an item in another Framework as an Exemplar.

Elaboration
We have discussed informally the idea of 'vocabulary' frameworks. I propose we allow Exemplar as an option for making associations by default as well as keep the "add URL" option currenlty in place.

https://github.com/opensalt/opensalt/blob/9a7cd61a5d647c8fd7ef1701acac4d4ab71d66f0/assets/js/cftree/view-edit.js

/** Add an association */
apx.edit.prepareAssociateModal = function() {
// add an option for each association type to the associationFormType select
for (let i = 0; i < apx.assocTypes.length; ++i) {
if (apx.assocTypes[i] !== "Exemplar" && apx.assocTypes[i] !== "Is Child Of") {
$("#associationFormType").append('' + apx.assocTypes[i] + '');
}
}

proposed solution:
Just remove "apx.assocTypes[i] !== "Exemplar"" and the exemplar path will still be a URI?

[brandonopened]

@jmarks this came to light as I was thinking about our conversations around types of other frameworks. Makes sense to me even with say Smarter Balanced to have a framework of example questions etc and be able to associate them as task model exemplars.

I removed Exemplar so the code looks like this now:
/** Add an association */
apx.edit.prepareAssociateModal = function() {
// add an option for each association type to the associationFormType select
for (let i = 0; i < apx.assocTypes.length; ++i) {
if (apx.assocTypes[i] !== "Is Child Of") {
$("#associationFormType").append('' + apx.assocTypes[i] + '');
}
}

however i must be missing something because when i make an exemplar it does this:

so i'll have to wait a couple weeks for this to be done by a real developer.