implement /packages/{name} as its own route

A few things added with this commit:

- aurweb.packages.util
    - A module providing package and pkgbase helpers.
- aurweb.template.register_filter
    - A decorator that can be used to register a filter:
      @register_filter("some_filter") def f(): pass

Additionally, template partials have been split off a bit
differently. Changes:

- /packages/{name} is defined in packages/show.html.
- partials/packages/package_actions.html is now
  partials/packages/actions.html.
- partials/packages/details.html has been added.
- partials/packages/comments.html has been added.
- partials/packages/comment.html has been added.
- models.dependency_type additions: name and id constants.
- models.relation_type additions: name and id constants.
- models.official_provider additions: base official url constant.

Signed-off-by: Kevin Morris <kevr@0cost.org>

templates/packages/show.html

@@ -0,0 +1,23 @@
+{% extends "partials/layout.html" %}
+
+{% block pageContent %}
+    {% include "partials/packages/search.html" %}
+    <div id="pkgdetails" class="box">
+        <h2>{{ 'Package Details' | tr }}: {{ pkgbase.Name }} {{ pkgbase.packages.first().Version }}</h2>
+
+        {% set result = pkgbase %}
+        {% include "partials/packages/actions.html" %}
+
+        {% set show_package_details = True %}
+        {% include "partials/packages/details.html" %}
+
+        <div id="metadata">
+            {% include "partials/packages/package_metadata.html" %}
+        </div>
+    </div>
+
+    {% set pkgname = result.Name %}
+    {% set pkgbase_id = result.ID %}
+    {% set comments = comments %}
+    {% include "partials/packages/comments.html" %}
+{% endblock %}