Loading item template

[cgross]

This PR builds on the work done by @jseminck in #451. This PR fixes the merge conflicts and an issue using the loading template in multiple collections. It also tweaks the demo app to remove the loading template from the initial example input and moves it to the second one with the remote collection.

[ilyaskarim]

This is not working for me, any idea what I am doing wrong here, my values function looks like:

async function (text, cb) {
  let handler = async () => {
    try {
      let response = await editor.wsf_term.SearchTerms(null, text)
      if (response) {
        cb(response.map((c) => {
          const label = TermTypeApiLabels[termTypesReversed[c.TermType]]
          const key = `<span class="wsf-term-select" ><span class="wsf-term-select-shortcut" >${c.ShortcutKey}</span>${termTypesReversed[c.TermType]}: ${c[label]}</span>`;
          return {
            ...c,
            key,
            value: c.Id,
          }
        }))
      }
    } catch (e) {
      console.log(e);
    }
  }
  clearInterval(window.SearchTermsTimeout);
  window.SearchTermsTimeout = setTimeout(handler, 300);
}

and loading template

loadingItemTemplate: "<p>...loading<p>",