#442: show ng-letter as discussion avatar when user has no custom avatar
#442: show ng-letter as discussion avatar when user has no custom avatar

PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile,PowerlineApp/powerline-mobile