const in appinfo for using in templates

src/__main__.py

@@ -386,6 +386,7 @@ def main():
         "otherapps": config["otherstates"],
         "tags": config["appconfig"]["tags"],
         "config": config["appconfig"]["config"],
+        "const": config['appinfo']['const'],
     }
 
     os.chdir(os.path.expanduser("~"))

src/resources/appinfo.yml

@@ -41,6 +41,12 @@ properties:
             additionalProperties: false
             type: object
         description: A jsonschema defining the configuration that should be given to the application.  Defaults will be filled in.
+    const:
+        type: object
+        default: {}
+        description: Extra constant variables that can be used in templates, centrally defined in this config
+        additionalProperties:
+            type: string
     templatefiles:
         type: array
         default: []