Feature/#15 clean plurals

[Quicksaver]

Closes #15:

• Backport clean plurals in admin sidebar from FESAgency (https://github.com/marzeelabs/fesagency/pull/25)
• No more third-party hard copies! Build dependencies (jQuery, slick, js-yaml) into JS with webpack and compile/minify with babel
  • Updated those dependencies to the latest versions, for no reason other than those were what npm installed by default.
• New scripts folder structure:
  • .js files in scripts/site/ are bundled into static/js/site.min.js to use in all general pages;
  • .jsfiles in scripts/admin/ are bundled into static/admin/admin.min.js to use in the CMS admin interface pages.
• Changed footer hardcoded section into configurable content (both en and pt).
• Unrelated: correctly preview "people-pt" content.

To Do - this will likely need porting into current in-development projects (uhub and FESAgency).

[Quicksaver]

Both scripts and scripts-admin gulp tasks can take over 10 seconds to complete, although the resulting file sizes are equivalent to before. Definitely worth investigating before merging.

[Quicksaver]

Longer times are because the compilers now transverse node_modules looking for matches.