Minerva already overrides the text label for the Home menu item.
To allow other extensions to override it again, we can also consult
the msg key.
Bug: T291568
Change-Id: I3107a6d1e6ace26c7ab9c49c49768d2adcda8792
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
