Saving/reading hypsography with InputOutput is not fully automated

Right now, the `InputOutput` module has to know about the details of the hypsography to save/read it from file. Adding a new adaption requires adjusting this module. It should be possible to automate this.

Start by tracing the InputOutput module's current hypsography save and read paths and identifying where hypsography-specific details are hard-coded. Define how a new adaption should work without changes to InputOutput, then add coverage for saving and reading existing and newly supported adaptions.

Written by the indexing model from the issue text.