BPHY23: Commit PsiPlusPsiCascade class

Two updates:

1. Modified BPHY23.py to include

• Psi(2S) + Psi(2S) -> mu mu Jpsi pi pi -> 4mu + pi pi
• Upsilon(2S) + Upsilon(2S) -> mu mu Upsilon pi pi -> 4mu + pi pi
• Psi(2S) + Upsilon(2S) -> mu mu Upsilon pi pi -> 4mu + pi pi
• Upsilon(2S) + Psi(2S) -> mu mu Jpsi pi pi -> 4mu + pi pi
• mu mu (non-resonant) + Upsilon(2S) -> mu mu Upsilon pi pi -> 4mu + pi pi

2. Added PsiPlusPsiCascade class to include

• Psi(2S) + Psi(2S) -> Jpsi pi pi Jpsi pi pi -> 4mu + 4pi
• Psi(2S) + Upsilon(2S) -> Jpsi pi pi Upsilon pi pi -> 4mu + 4pi
• Upsilon(2S) + Upsilon(2S) -> Upsilon pi pi Upsilon pi pi -> 4mu + 4pi

JIRA ticket: https://its.cern.ch/jira/browse/ATLBPHYS-219

Sincerely, -Xin