Please support md-icon inside md-avatar

[CxRes]

Currently, if I want to have an icon inside an avatar, I have to align it manually.

I believe this should be supported within angular material because this example is defined in the material design spec. See section Tile Content in http://www.google.com/design/spec/components/lists.html#lists-content

[ajd394]

I ran into this issue too!

[ThomasBurleson]

A Pull Request to submit this feature would be welcomed.