Support app configuration loading from envvar

.gitignore

@@ -1 +1,4 @@
 *.pyc
+*.cfg
+*.db
+*.sqlite3

bitvend/__init__.py

@@ -1,4 +1,5 @@
 import flask
+import os
 
 from bitvend.processor import PaymentProcessor
 from bitvend.mdb import BitvendCashlessMDBDevice
@@ -29,6 +30,8 @@ def bitvend_user_loader(username, profile=None):
 def create_app():
     app = flask.Flask(__name__)
     app.config.from_object('bitvend.default_settings')
+    app.config.from_pyfile(os.environ.get('BITVEND_SETTINGS', ''), silent=True)
+
 
     db.init_app(app)
     spaceauth.init_app(app)

deployment/bitvend.service

@@ -5,6 +5,7 @@ After=pigpiod.service
 [Service]
 Type=simple
 User=bitvend
+Environment=BITVEND_SETTINGS=bitvend.cfg
 WorkingDirectory=/var/bitvend
 ExecStart=/usr/bin/python3 -u /var/bitvend/bitvend.py
 Restart=on-failure