Bugfix probmax issue for TENSOR daughter in EvtSSD_DirectCP model.

Summary:
This revision solves the task T208 (related also to T207).

Fixed initialization bug in EvtSSD_DirectCP model.

Calculation of amplitude moved to dedicated calcAmp function. Got rid of a few static variables along the way.

Changed reference PDL ids to static const to avoid recreation.

Use declare variables inside loops as const.

Modified calcAmp to be void const. Removed unneeded indentation if level in calcAmp. Implement updating of theta_max at initialisation.

Added comment for Tensor case in calcAmp.

Test Plan: Check output of relevant tests. Histograms should not vary (except for Tensor case).

Reviewers: tlatham

Reviewed By: tlatham

Subscribers: jback, kreps, tlatham

Tags: #evtgen

Differential Revision: https://phab.hepforge.org/D92