Rather than hardcoding the icons for all our menu items
let's use the definitions in core.
This also makes it easier for us to deprecate the
MobileMenu hook in future.
Rejoice at all the code this removed!
Bug: T291568
Change-Id: I69b5ca13aee018982a5ea28677d4a37e663235d4
isRegistered() is a method in the much more narrow UserIdentity
interface. This change makes it easier to move code away from the
problematic User "god" class in core.
Change-Id: I99cb72591f073568f84bd1fd436381f3f11f3140
