This commit removes most of the default launchers, which are now
superseded by the interactive component addition feature of the '+'
menu.
We keep the chroot components because we cannot easily create chroot
instances interactively yet.
The usb_devices_rom is still needed because its configuration is meant
to be edited at runtime.
It also adds a 'themed_wm' launcher to make the initial sculpt
experience easier. For knowledgeable users, the index contains all
ingredients needed to build a multi-component window manager manually.
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