Task #551092: Add Somali flag icon.

Fetched SVG of the Somalian flag from Wikipedia[1], ran it through
`convert`[2] and `pngcrush`[3].

[1] https://en.wikipedia.org/wiki/File:Flag_of_Somalia.svg
[2] convert -resize x12 -sigmoidal-contrast 10,50%
[3] pngcrush -brute -fix -force -reduce