Comment 2 for bug 1550670

Alright so it sounds like this is what we need to do. Granite.Widgets.Avatar needs to be able to accept either a string or an image, but one of these should be mandatory. No more mystery man. Given a string, it should...

Get letters to display:

* Take the first two letters of the first two words. So if you give it "Gordon Ramsey", it takes "GR". If you give it "<email address hidden>" it takes "D".

Get a color to use:

* Take the first 3 characters of the string and convert that to hex.
* convert the hex to a HSL color.
* Maximize the saturation.

Getting the color with this formula instead of randomly means that given the same string you'll get the same filler-avatar across apps. So Gordon Ramsey is blue in Mail, Calendar, the session menu, the users plug, etc.