Initial commit: boarding pass to AirTrail pipeline

Photograph/screenshot a boarding pass, decode its BCBP barcode (PDF417/
Aztec/QR/DataMatrix), fetch the historical flight track from FlightAware
the day after the flight, stage it for review, and write it into AirTrail
via its REST API on approval. ntfy notifications carry signed
Approve/Deny/Investigate actions.

routes_settings.py

@@ -0,0 +1,31 @@
+"""GET/POST /settings - notification backend configuration, plus a
+send-test-notification action."""
+
+from flask import Blueprint, redirect, render_template, request, url_for
+
+import models
+import notifier
+
+bp = Blueprint("settings", __name__)
+
+FORM_FIELDS = ["ntfy_server_url", "ntfy_topic", "ntfy_auth_token", "daily_run_time"]
+
+
+@bp.route("/settings", methods=["GET", "POST"])
+def settings():
+    message = None
+    if request.method == "POST":
+        if request.form.get("action") == "test":
+            notifier.get_notifier().send(
+                title="Test notification",
+                body="This is a test notification from boarding-pass-pipeline.",
+                url=None,
+            )
+            message = "Test notification sent."
+        else:
+            for f in FORM_FIELDS:
+                if f in request.form:
+                    models.set_setting(f, request.form[f].strip())
+            message = "Settings saved."
+
+    return render_template("settings.html", settings=models.get_all_settings(), message=message)