Small updates and fixes

Created by: Re4son

• arm64 looks complete now so we can move away from using armhf rootfs on arm64
• Use latest nethunter app which sets SELinux to permissive mode early on during startup, no individual kernel patches required anymore
• Add wallpaper for Gemini PDA
• Fix sed command to add _apt user to inet group irrespective of the user ID
• Update build script to install latest libapache2-mod-php7.3 instead of *7.2