Implement YAML config loader

config/app.example.yml

@@ -0,0 +1,23 @@
+# This is an example config file for MailAccountAdmin.
+# Copy this file to /config/app.yml and change as needed.
+# Settings that are commented out represent the default values.
+
+# -- App settings
+# appTitle: MailAccountAdmin
+# environment: production
+# debug: false
+# timezone: UTC
+# dateTimeFormat: r
+
+# -- Twig settings
+twig:
+  # Cache directory for Twig templates (default: unset, which means no cache is used)
+  cacheDir: .twig.cache
+
+# -- Database settings
+database:
+  host: localhost
+  port: 3306
+  name: mailusers
+  username: mailaccountadmin
+  password: very_secret_password