Prepare addition/replacement of p-model example data - attempt 2

[fabern]

This reapplies "Merge pull request #322 from geco-bern/update-vignettes-with-gmd-paper" for another pull request.

Background:
These changes have been reverted in the main branch to avoid overwriting the documentations website.

We have meanwhile changed the main branch to distinguish between release and development documentations, effectively generating two documentations websites: http://geco-bern.github.io/rsofun/dev/ and http://geco-bern.github.io/rsofun/

Thus we now make another attempt at the PR to

• update the model example data sets,
• make changes to calib_sofun, and
• update the formats of the drivers and validation data sets

[fabern]

• As discussed in person, the format of the validation data set and the calib_sofun() should be changed to correspond to the structure: