Complete rewrite (#1)

A complete rewrite of the gallery plugin:

* Using flexbox
* Using lightweight JS for lightbox to avoid anchor links, and allow full rotation
* Add slideshow as an additional field
* Make many more things configurable
* Better support for dirs, allow mixed paths
* Translatable captions for many files using metadata files
* SCSS instead of CSS

Reviewed-on: #1
Co-authored-by: Max Mehl <mail@mehl.mx>
Co-committed-by: Max Mehl <mail@mehl.mx>

layouts/partials/lightbox.html

@@ -0,0 +1,24 @@
+{{- $imgs := .imgs -}}
+{{- $galno := .galno -}}
+<div class="snap-lightbox" id="snap-lightbox-{{ $galno }}">
+  {{- range $i, $img := $imgs }}
+  <div class="snap-lightbox-inner">
+    <div class="snap-numbertext">{{ add $i 1 }} / {{ len $imgs }}</div>
+    <img
+      src="{{ relURL $img.src }}"
+      {{ range $attr, $value := $img.html -}}
+        {{ safeHTMLAttr $attr }}={{ $value }}
+      {{ end -}}
+    />
+    {{- with $img.html.title }}
+      <div class="snap-caption">{{ . }}</div>
+    {{- end }}
+  </div>
+  {{- end -}}
+
+  <!-- Close and Next/previous controls -->
+  <span class="snap-close" onclick="closeLightbox({{ $galno }})">&times;</span>
+
+  <a class="snap-prev" onclick="moveLightboxItem({{ $galno }}, -1)"><span>&#10094;</span></a>
+  <a class="snap-next" onclick="moveLightboxItem({{ $galno }}, 1)"><span>&#10095;</span></a>
+</div>