Fix/exp design hdf5

Fix issues with the read-in of the experimental design from an existing hdf5-file.

• No re-sampling when hdf5 file is read in
• Resample if Y is given and no X is given! Then also HAVE to rerun the model
• If X is given, set sampling_method to 'user'
• If X and Y are given, use the given combination!
• Add warnings if method is changed, and when Y is being overwritten!

Checks:

• Add tests that check for these corrections
• Note in changelog