port over base HTML layout from PHP to FastAPI+Jinja2

+ Mounted static files (at web/html) to /static.
+ Added AURWEB_VERSION to aurweb.config (this is used around HTML
  to refer back to aurweb's release on git.archlinux.org), so we
  need it easily accessible in the Python codebase.
+ Implemented basic Jinja2 partials to put together whole aurweb
  pages. This may be missing some things currently and is a WIP
  until this set is ready to be merged.
+ Added config [options] aurwebdir = YOUR_AUR_ROOT; this configuration
  option should specify the root directory of the aurweb project.
  It is used by various parts of the FastAPI codebase to target
  project directories.

Added routes via aurweb.routers.html:
    * POST /language: Set your session language.
    * GET /favicon.ico: Redirect to /static/images/favicon.ico.
        * Some browsers always look for $ROOT/favicon.ico to get an icon
          for the page being loaded, regardless of a specified "shortcut
          icon" given in a <link> directive.
    * GET /: Home page; WIP.

* Updated aurweb.routers.html.language passes query parameters to
  its next redirection.

When calling aurweb.templates.render_template, the context passed should
be formed via the aurweb.templates.make_context. See
aurweb.routers.html.index for an example of this.

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

templates/partials/set_lang.html

@@ -0,0 +1,28 @@
+<div id="lang_sub">
+    <form method="post" action="/language">
+        <fieldset>
+            <div>
+                <select id="id_setlang" name="set_lang">
+                    {% for domain, display in languages.items() %}
+                    <option
+                        value="{{ domain }}"
+                        {% if language == domain %}
+                        selected="selected"
+                        {% endif %}
+                    >
+                        {{ display }}
+                    </option>
+                    {% endfor %}
+                </select>
+
+                <!-- Pass our current url path as next. -->
+                <input type="hidden" name="next" value="{{ request.url.path }}">
+
+                <!-- Pass query_params over to /language via POST. -->
+                <input type="hidden" name="q" value="{{ request.query_params }}">
+
+                <input type="submit" value="Go">
+            </div>
+        </fieldset>
+    </form>
+</div>