Fix favicon.ico.

Recreate it from favicon.png; include a 32x32 and a 16x16 one.
Losslessly compress PNG files.

Before: 382 KB (391.968 bytes)
After:  233 KB (239.145 bytes)
Convert the remaining images to 8-bit.

Before: 233 KB (239.145 bytes)
After:  216 KB (221.949 bytes)
Merge pull request #273 from XhmikosR/images

Fix favicon.ico and compress images