harmonize arguments project_as_ppi() and integrate_to_ppi()

[adokter]

The specification of the projection raster is different for these two functions, which is cumbersome if you want to plot the results of the two functions next to each other.

• [ ] refactor project_as_ppi, such that grid_size argument no longer parses spatial objects (we do not want different classes parsed through the same argument)
• [ ] harmonize range_max argument
• [ ] harmonize grid_size argument
• [ ] there is more ...

[adokter]

Should tackle this issue first before writing its associated unit tests.