Add pre-configured app source lists

[omeritzics]

Such as:

• Game emulators (https://github.com/omeritzics/Updatium-Emulation-Pack)
• Messaging apps
• Internet browsers
• Productivity apps
• Essential apps
• De-Googling pack
• Icon packs
• Custom FOSS launchers

Todo:

• Find/make lists to add
• Implement the built-in list feature in Updatium
• Make proper built-in list guidelines