Concatenated all JS into a single file (#624)

no issue

- moved large inline JS from templates into separate JS files
  - floating header
  - gallery card support
- use `gulp-concat` to concatenate all JS files into a single `built/casper.js` file
- reduces external JS file requests from 3 (jquery, infinite-scroll.js, jquery.fitvids.js) down to 2 (jquery, casper.js) and reduces page size by removing repeated inline code

post.hbs

@@ -145,67 +145,9 @@ into the {body} of the default.hbs template --}}
 {{!-- The #contentFor helper here will send everything inside it up to the matching #block helper found in default.hbs --}}
 {{#contentFor "scripts"}}
 <script>
-
-// NOTE: Scroll performance is poor in Safari
-// - this appears to be due to the events firing much more slowly in Safari.
-//   Dropping the scroll event and using only a raf loop results in smoother
-//   scrolling but continuous processing even when not scrolling
-$(document).ready(function () {
-    // Start fitVids
-    var $postContent = $(".post-full-content");
-    $postContent.fitVids();
-    // End fitVids
-
-    var progressBar = document.querySelector('#reading-progress');
-    var header = document.querySelector('.floating-header');
-    var title = document.querySelector('.post-full-title');
-
-    var lastScrollY = window.scrollY;
-    var lastWindowHeight = window.innerHeight;
-    var lastDocumentHeight = $(document).height();
-    var ticking = false;
-
-    function onScroll() {
-        lastScrollY = window.scrollY;
-        requestTick();
-    }
-
-    function onResize() {
-        lastWindowHeight = window.innerHeight;
-        lastDocumentHeight = $(document).height();
-        requestTick();
-    }
-
-    function requestTick() {
-        if (!ticking) {
-            requestAnimationFrame(update);
-        }
-        ticking = true;
-    }
-
-    function update() {
-        var trigger = title.getBoundingClientRect().top + window.scrollY;
-        var triggerOffset = title.offsetHeight + 35;
-        var progressMax = lastDocumentHeight - lastWindowHeight;
-
-        // show/hide floating header
-        if (lastScrollY >= trigger + triggerOffset) {
-            header.classList.add('floating-active');
-        } else {
-            header.classList.remove('floating-active');
-        }
-
-        progressBar.setAttribute('max', progressMax);
-        progressBar.setAttribute('value', lastScrollY);
-
-        ticking = false;
-    }
-
-    window.addEventListener('scroll', onScroll, {passive: true});
-    window.addEventListener('resize', onResize, false);
-
-    update();
-
-});
+    $(document).ready(function () {
+        var $postContent = $(".post-full-content");
+        $postContent.fitVids();
+    });
 </script>
 {{/contentFor}}