MB 11: Add Mullvad branding to the NSIS installers

Merge Info

Related Issues

• privacy-browser#11
• privacy-browser#86

Issue Tracking

• Link resolved issues with appropriate Release Prep issue for changelog generation

Change Description

Adapts the changes from tor-browser-build!670 (merged) to Mullvad Browser.

(now I've changed from Mullvad VPN AB to Mullvad AB, according to Rui's comment in the issue)