unify use of 'src' and 'url' attributes

[JoernT]

policy will be: if it's consuming a resource it should be 'src' - otherwise url

• [x] fx-fore uses 'src'
• [x] fx-control uses 'url' - now src since 2.0.0
• [ ] fx-load uses 'url' - will stay but might be two use cases
• [x] fx-submission uses 'url' - will stay

should be unified

[JoernT]

done for fx-control. url is srcsince 2.0.0