Load components for Arch Linux

[City-busz]

Load the "core" and "extra" components, which contain most of the icon data on Arch Linux.

See also the downstream report:
https://bugs.archlinux.org/task/61157

[ximion]

Seems fair, although I really do wonder whether we should at least put this into the distro-specific abstraction now.
I actually wanted to do an asgen release today, but deferred it as the planned feature required a bit more work. Potentially, this particular case is also one to address properly in the next release.
I'll look into it.
For now, thank you for the patch, and let's merge it until something better is implemented.