Small tweaks on Implosion

• Fixes #143 (closed) by spliting the deathtriggers in 2 parts (one that instakills and one on the edge that deals 50 dmg) and by indicating danger with some lightning effects.
• Fixes #141 (closed), #142 (closed) and #145 (closed).
• Re-align a few trims so they look better and are symmetrical on the 2 bases.
• Fix a tiny missing texture in the blue corridor.