Allow file:/// URL for JSON data for online quote update

[dietmarb01]

Is your feature request related to a problem? Please describe.
A JSON file with quotes and possibly other information can be prepared outside PP. Consumption of this data nevertheless requires a web-server to expose this file over HTTP. It would be great to be able to use a "file:///" URL to specify the location of this data.

Describe the solution you'd like
Allow and support "file:///" URL in the definition of a JSON source for online quote update.

Describe alternatives you've considered
Roll your own web-server (each user individually).

Additional context
None.