computation of the projection variables G,D, C should have their own function

[aliutkus]

right now, the code in _project and _project_images is very redundant for no reason,

furthermore, there are cases where we want to compute these variables without doing the actual filtering, as I believe we should do for the frame_wise eval

[bmcfee]

IIRC the reason for this was to keep the translation from the matlab implementation as direct as possible. Maybe @dawenl can comment?

[aliutkus]

I am in the process of working on these two recent issues I opened, I will keep you posted !