[NEW FEATURE] Trim filters to the minimum in get_mr_filters

[zaccharieramzi]

Is your feature request related to a problem? Please describe.
I'm always frustrated when using get_mr_filters because it gives me huge filters if I have a huge data_shape (in my case (512, 512)). The convolution then takes so much time.

Describe the solution you'd like
I would like the filters to be trimmed to the minimum so that the convolutions take less time (also it would additionally decrease memory reqs but it's not really an issue).

Describe alternatives you've considered
I could trim them afterwards outside the function, but I think it makes sense to trim them in it.

[sfarrens]

Resolved in #51