Add "retro" default skin resources

[cl8n]

the idea of this skin is to look like 2008, around the time that main gameplay settled into the design that would last until 2013. however the files aren't necessarily all the same as in a 2008 client because I preferred later versions as long as they only fixed bugs or applied minor tweaks to 2008. also, some elements just aren't that old, but I included them as long as they differed from 2013.

specifically, most files in this PR come from XNB/WAV files in b20121119. the following are from b1652: comboburst-0, cursor, cursortrail, star2, taiko*. these versions are not significant beyond being publicly archived and allowing me to build the skin with the above criteria

skin.ini is hand-written since that's not an actual file shipped with the game, but I did my best to make it accurate.

misc notes

• files included: everything lazer can use, plus resources for countdown, combo burst, and geki/katu (see Sync default legacy skin resources with implementation #380)
• I included both old combobursts, despite those not existing together at any one point in time
• many elements are not included due to staying identical in 2013: almost all samples, all fruits, all mania elements, and pippidon
• menu-background is not included because it seems more tied to the intro screen in lazer

texture script (snippet)

https://github.com/cl8n/xnb-reader

xnb-read "$tmp_path/$xnb_filename" --first-mip --pipe \
	magick -depth 8 -size {width}x{height} bgra:- -alpha off-if-opaque -strip \
	"$out_path/${xnb_filename%.xnb}.png"