Chane NSI install dir/key from "Bitcoin" to "Elements"

Add updated bitcoin icon

Changing Elements Icon to just the graphic without text, fixing issue…

… with gitian builds on icon, removing color change based on testnet for Elements, and compatible svg with build script.

v0.18.1.7

v0.18.1.6

v0.18.1.5

Elements 0.18.1.3

Elements 0.18.1.3 RC4