Add fallback for when the user isn't running the framework

**Is your feature request related to a problem? Please describe.**
If user is using frank-flow in standalone or as demo, the elements can't get fetched.

**Describe the solution you'd like**
Use frankdoc.frankframework.org as fallback

- [ ] Json file
- [ ] Elements (gui)

**Describe alternatives you've considered**
- frank4example
- Include files