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/slideshow.html

@@ -0,0 +1,21 @@
+{{- $imgs := .imgs -}}
+{{- $galno := .galno -}}
+<div class="snap-slideshow" id="snap-slideshow-{{ $galno }}" style="--columns:1;--min-width:0px;--gap:0px;--slideshow-width:{{ default "100%" .width }};--cursor:{{ .cursor }};--aspectratio:{{ safeCSS (default "16/10" .aspectratio) }};">
+  {{- range $i, $img := $imgs }}
+  <div class="snap-image">
+    <div class="snap-numbertext">{{ add $i 1 }} / {{ len $imgs }}</div>
+    {{- with $img.html.title }}
+      <div class="snap-caption">{{ . }}</div>
+    {{- end }}
+    <img
+      src="{{ relURL $img.src }}"
+      {{ range $attr, $value := $img.html -}}
+        {{ safeHTMLAttr $attr }}={{ $value }}
+      {{ end -}}
+      onclick="openLightbox({{ $galno }});openLightboxItem({{ $galno }}, {{ add $i 1 }});" />
+  </div>
+  {{- end }}
+
+  <a class="snap-prev" onclick="moveSlideshowItem({{ $galno }}, -1)"><span>&#10094;</span></a>
+  <a class="snap-next" onclick="moveSlideshowItem({{ $galno }}, 1)"><span>&#10095;</span></a>
+</div>