[z2007] When GM is invisible use a transparency visual aura

Based on TC commit by DDuarte, ideas by Kretol and Aokromes

Add config setting GM.InvisibleAura to configure the to be used aura

Signed-off-by: Schmoozerd <schmoozerd@scriptdev2.com>

(cleaned version of fc42a48)

(based on commit [s1607] - b74a4f1)