more and better debugging output for particles

The current debugging code that prints out debugging information for specific particles is a bit outdated; it still uses a plain printf instead of one of the macros, and it does not include any of the subgrid variables.

This MR adds output for subgrid variables in the same way as is done for the hydro variables: by calling a model specific debug function. These functions are called in turn after the original call to hydro_debug_particle.

As an additional improvement, all debug functions now use warning to guarantee immediate output to the standard error. And all messages include the label [PIDxxxxxxx] so that they can be grepped in large output files.