Move galleries to collection, generate map and slideshow on build, stop using loopdir plugin, update templates accordingly

_config.yml

@@ -25,6 +25,20 @@ previous_page: '← Vorige pagina'
 next_page: 'Volgende pagina →'
 mentioned_in: 'Komt voor in:'
 
+# collections
+collections:
+    gallery:
+        output: true
+        permalink: /:collection/:name/
+
+# defaults
+defaults:
+    -
+        scope:
+            type: gallery
+        values:
+            layout: gallery-list
+
 # other
 gems: [jekyll-paginate]
 markdown: rdiscount
@@ -32,4 +46,5 @@ rdiscount:
     extensions: [smart]
 exclude:
 - LICENSE
-- README
+- README
+array: []