Summon2 translator

A new translator for working with Summon 2.0 and its endless scroll weirdness. It gets data for all the references that have been loaded on the page. It counts the number of refs on the page, queries Summon's API to get that same number back, sorts the data into the same order as shown on the page, and then populates the items. (It has to get 10 refs from the API at a time because that's how Summon loads them on the page. Trying to get more in a single call actually generates a different result set, strangely enough.)
Add license block. See https://github.com/zotero/translators/blob/master/Twitter.js#L18 for sample