Add function for padded convolutions

Necessary for the component optimization functionality in Radler.

This same functionality is already used in Radler's multiscale processing (the code is almost literally from there, but with added tests), so once this is merged that code can be refactored a little bit.

assigned to @offringa

changed the description

requested review from @veldhuis

Looks good and makes sense to me Just 2 very minor comments.

resolved all threads

approved this merge request

merged

mentioned in commit 7628fc36