Fix dump of checkpoint files

Fix dump of checkpoint files

With the addition of the MdModules and the modular checkpointing,
`gmx dump -cp` would end with an error when either of the two was
written to checkpoint. Reason was that the function dumping
checkpoint files was not aware of the additional blocks present.
As the new functionality checkpoints at the end of the files, the
remainder of the information was printed anyway, but the call ended
with an error.

This adds the two new checkpointing blocks to the function used
by gmx dump, and prints the kv-tree they are based on. To achieve
this, the kv-tree printing functionality had to be expanded to
allow for arrays of objects.

Finally, this change also fixes a wrong comment in the modular
simulator checkpoint helper - checkpointing happens on top of the
integration step, so _before_ the last step.