Make D-HYDRO compatible and default

[kdberends]

Is your feature request related to a problem? Please describe.
Currently FM2PROF outputs SOBEK 3 files by default. SOBEK3 will be phased out in favour of D-HYDRO 1D.

Describe the solution you'd like
Output D-HYDRO 1D files by default. Support SOBEK 3 as a legacy option.

Describe alternatives you've considered
There are no alternatives

Additional context
The timing to phase out SOBEK3 is currently unknown, but expected in 2-3 years.

[kdberends]

Expected work:

• Refactor export.py to support multiple output files in a more structured way than currently implemented. E.g. split current classes into more maintainable classes per output format.
• Create functionality and test on exporting correct format of D-Hydro input files.

Retire old unused format:

• "test format"
• the legacy "sobek3" format.

After refactoring support two output files:

• Sobek 3 (currently named "dflow1d" in the code. Rename this to "sobek3")
• dflow1d2d format (new)