Raven filter

[neon60]

• Add Raven filter to strip.py
• Add Raven filter unit tests
• Add Raven filter performance tests

[dkazanc]

thanks @neon60. I've also added you to the contributors list so you can create branches from httomolibgpu directly. In that case the CI of ours that run tests should work (I suspect that it is a reason for the current failure). I will test the method on a real data.

[namannimmo10]

Looks good, thank you Istvan!