revert !58 category paginating: it fails with stacktrace

I'll have to revert this, I'm out of ideas.  Its a strange issue.
Basically the `date_to_xmlschema` filter in __pages/feed.xml_ is
getting a list of `Page` instances instead of a `datetime`.

!58 (comment 361936012)

This reverts commits:
1e9a5a4c
fa7e69e7

_layouts/category-packages.html

@@ -2,24 +2,14 @@
 layout: page
 title: " "
 permalink: filled_by_script
-pagination:
-  enabled: true
-  collection: filled_by_script
-  per_page: 30
-  trail:
-    before: 4
-    after: 4
-  permalink: '/:num/'
-  title: ':title'
-  sort_field: 'last_updated'
-  sort_reverse: true
 ---
 
+{% assign app_category_escaped = page.app_category | escape %}
+{% assign filtered_packages = site.packages | where_exp: "item", "item.categories contains app_category_escaped" | sort: "last_updated" | reverse %}
+
 <h3>{{ site.data.strings.app_categories[page.app_category] }}</h3>
 <div id="package-list">
-  {% for package in paginator.posts %}
+  {% for package in filtered_packages %}
     {% include package-list-item.html package=package %}
   {% endfor %}
-
-  {% include_cached browse-paginator-navigation.html paginator=paginator permalink=page.dir %}
 </div>

lib/fdroid/App.rb

@@ -85,10 +85,6 @@ module FDroid
       return code
     end
 
-    def categories
-      return field('categories')
-    end
-
     # Generates a hash of dumb strings to be used in templates.
     # If a specific value is not present, then it will have a nil value.
     # If a value can be localized, then it will choose the most appropriate

lib/jekyll/FDroidCategoryDetailPage.rb

@@ -20,20 +20,19 @@ module Jekyll
     # @param [Jekyll::Site]  site
     # @param [string]  base
     # @param [string]  app_category
-    # @param [string]  app_category_id
-    def initialize(site, base, app_category, app_category_id)
+    def initialize(site, base, app_category)
       @site = site
       @base = base
       @dir = 'categories'
 
       # Avoid special characters in URL, otherwise language support doesn't work
-      @name = "#{app_category_id}/index.html"
+      app_category_url = Utils.slugify(app_category)
+      @name = "#{app_category_url}/index.html"
 
       self.process(@name)
       self.read_yaml(get_layout_dir, 'category-packages.html')
       self.data['app_category'] = app_category
       self.data['permalink'] = "/categories/#{app_category_id}/"
-      self.data['pagination']['collection'] = app_category_id
     end
 
     def get_layout_dir()

lib/jekyll/FDroidPackageDetailGenerator.rb

@@ -37,21 +37,8 @@ module Jekyll
           site.config["sass"]["load_paths"] << (File.expand_path "../../_sass", File.dirname(__FILE__))
         end
 
-        # Enable pagination
-        if site.config["pagination"].nil? || site.config["pagination"].empty?
-          site.config["pagination"] = Hash.new
-        end
-        site.config["pagination"]["enabled"] = true
-
         index = FDroid::IndexV1.download(site.config["fdroid-repo"], site.active_lang || 'en_US')
 
-        # Generate collection and detail page for every category
-        site.config["app_categories"].each do |app_category|
-          app_category_id = Utils.slugify(app_category)
-          site.collections[app_category_id] = Collection.new(site, app_category_id)
-          site.pages << FDroidCategoryDetailPage.new(site, site.source, app_category, app_category_id)
-        end
-
         # Generate detail page for every package
         site.collections["packages"] = Collection.new(site, "packages")
         index.apps.each do |package|
@@ -62,17 +49,11 @@ module Jekyll
           # https://gitlab.com/fdroid/jekyll-fdroid/issues/38
           site.pages << FDroidPackageDetailPage.new(site, site.source, package)
           site.collections["packages"].docs << FDroidPackageDetailPage.new(site, site.source, package)
+        end
 
-          package.categories.each do |app_category|
-            app_category_id = app_category.dup
-            app_category_id.sub!('&amp;', '&')
-            app_category_id = Utils.slugify(app_category_id)
-            if site.collections[app_category_id].nil?
-              puts("Warning: App '#{package.package_name}' has unknown category '#{app_category}', will be ignored")
-            else
-              site.collections[app_category_id].docs << FDroidPackageDetailPage.new(site, site.source, package)
-            end
-          end
+        # Generate category pages with filtered package list
+        site.config["app_categories"].each do |category|
+          site.pages << FDroidCategoryDetailPage.new(site, site.source, category)
         end
 
         # Generate browsing pages