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>

test/test_routes.py

@@ -0,0 +1,69 @@
+import urllib.parse
+
+from http import HTTPStatus
+
+import pytest
+
+from fastapi.testclient import TestClient
+
+from aurweb.asgi import app
+from aurweb.testing import setup_test_db
+
+client = TestClient(app)
+
+
+@pytest.fixture
+def setup():
+    setup_test_db("Users", "Session")
+
+
+def test_index():
+    """ Test the index route at '/'. """
+    # Use `with` to trigger FastAPI app events.
+    with client as req:
+        response = req.get("/")
+    assert response.status_code == int(HTTPStatus.OK)
+
+
+def test_favicon():
+    """ Test the favicon route at '/favicon.ico'. """
+    response1 = client.get("/static/images/favicon.ico")
+    response2 = client.get("/favicon.ico")
+    assert response1.status_code == int(HTTPStatus.OK)
+    assert response1.content == response2.content
+
+
+def test_language():
+    """ Test the language post route at '/language'. """
+    post_data = {
+        "set_lang": "de",
+        "next": "/"
+    }
+    with client as req:
+        response = req.post("/language", data=post_data)
+    assert response.status_code == int(HTTPStatus.SEE_OTHER)
+
+
+def test_language_invalid_next():
+    """ Test an invalid next route at '/language'. """
+    post_data = {
+        "set_lang": "de",
+        "next": "/BLAHBLAHFAKE"
+    }
+    with client as req:
+        response = req.post("/language", data=post_data)
+    assert response.status_code == int(HTTPStatus.BAD_REQUEST)
+
+def test_language_query_params():
+    """ Test the language post route with query params. """
+    next = urllib.parse.quote_plus("/")
+    post_data = {
+        "set_lang": "de",
+        "next": "/",
+        "q": f"next={next}"
+    }
+    q = post_data.get("q")
+    with client as req:
+        response = req.post("/language", data=post_data)
+        assert response.headers.get("location") == f"/?{q}"
+    assert response.status_code == int(HTTPStatus.SEE_OTHER)