Create theme for rEFInd boot screen

[marmarek]

rEFInd boot manager may be used to launch Qubes OS installation in UEFI mode (see #794 for details). It supports graphical menu, but require a theme there. I've configured "something", based on already existing graphics, but it doesn't look good...

Required files:

• background
• icons - may be the same for every entry, or separate for: "install", "verify disk and install", "rescue", "troubleshooting - verbose boot"
• optionally icons for standard actions: shutdown, reboot, exit

All the files are in http://github.com/qubesos/qubes-artwork repo.

@bnvk can you prepare those files? I guess it's very little work for you. Then I'd release next EFI-enabled image for testing really soon.

[marmarek]

Moving to backlog since we've abandoned rEFInd, at least for now.