Changes

Clubb organization part3 (#1306)

* More BFB movements

* Reworking where sigma_sqd_w and gamma_Skw_fnc are computed - this should all be BFB. Also fixing the G_unit test that was failing due to sigma_sqd_w issues

* Correcting arg list

* Fixes after rebase

* Making sigma_sqd_w_zt BFB vs master when using iiPDF_type=7 (new hybrid)

* Fixing python API

* Changing name of compute_xp3 to diagnose_xp3 and moving a1_coef and a3_coef calculation back into advance routines

* Fixes for GPU code