Convert images to 8bit.

david.png                     | Bin 10616 -> 6785 bytes
src/img/bg-david.png          | Bin 18050 -> 15544 bytes
src/img/dev-notsouptodate.png | Bin 3549 -> 2422 bytes
src/img/dev-outofdate.png     | Bin 3705 -> 2486 bytes
src/img/dev-uptodate.png      | Bin 3793 -> 2401 bytes
src/img/logo-david.jpg        | Bin 5527 -> 2136 bytes
src/img/notsouptodate.png     | Bin 3248 -> 2313 bytes
src/img/outofdate.png         | Bin 3609 -> 2323 bytes
src/img/unknown.png           | Bin 2871 -> 2356 bytes
src/img/uptodate.png          | Bin 3594 -> 2275 bytes

Total difference -17521 bytes.