Use WikiProject banner shell on draft talk pages

[NovemLinguae]

• Fix Implement WP:PIQA (put the article's class rating in the banner shell instead of in the wikiproject templates) #319
• Fix Multiple WikiProject banners should be collapsed in {{WikiProject banner shell}} #73
• In unit tests, switch from single quotes to backticks, for increased multi-line readability.
  • Enable ES6 in test files. Backticks are ES6.
• Always wrap WikiProject banners in {{WikiProject Banner Shell}}, even if it's just 1 banner. This improves maintainability by only having 1 code path instead of 2 (no banner shell code path, banner shell code path), and lets us close a couple of no banner shell code path tickets that as of this patch are fixed in the banner shell code path:
  • Fix When accepting, apply quality assessment to existing WikiProject banners #288
    • This is fixed because the banner shell now has the class
  • Fix Remove "class=draft" from WikiProject templates when submitting #115
    • This is fixed because the algorithm deletes all |class= except for the one in the banner shell
• Fix When accepting, unexpected line break between new WikiProject banners and old WikiProject banners #330
• Add test cases
• Handle an existing banner shell on the page
• Fix Deduplicate wikiproject banners #209
• Simplify the edit summary on draft talk pages to no longer include the count of banners added. For example, "Placing [[Wikipedia:Articles for creation|Articles for creation]] banner, adding 2 WikiProject banners" will now be "Placing [[Wikipedia:Articles for creation|Articles for creation]] banner, and possibly other banners"
• Complete rewrite of AFCH.addTalkPageBanners()
• Refactor AFCH.addTalkPageBanners() to remove 3 unnecessary parameters and to simplify its return values
• Create AFCH.removeDuplicateBanners() and add unit tests for it

Major existing bugs not fixed in this patch

• On the accept screen, existing WikiProject banners are not detected, so the WikiProject banners box never has any chips in it (probably On the accept screen, WikiProjects are not correctly detected when inside of {{WikiProject banner shell}} #185)
• Cannot remove a WikiProject (When accepting, de-selecting an existing WikiProject banner does not delete it from the draft talk page #329)

New bugs introduced by this patch (may fix later if they are common)

• Nested templates are likely to cause bugs
• Parameters in old banners or old shells may be deleted, overwritten with a simpler banner or shell