Minor fixes and bugs

• Improve user experience by moving initial media scan to background
• New command line argument --swupd-cert to pass to swupd
• Real-time updates of swupd progress during installation
• Code clean-up of unused swupd related functions
• Add system compatibility check to the Text-based installer
• Improve ISO booting process; colorize compatibility checks (pass/fail)
• Fix bug in ISO generation where some statuses were repeated
• New pop-up dialog while media is rescanned