float the build buttons as a horizontal bar over the game world and show key bindings inside build buttons

src/ui/HeaderBar.cpp

@@ -21,13 +21,6 @@
 #include "SpeedChangeRequestedEvent.h"
 #include "Tick.h"
 
-namespace
-{
-    // Item id of the building blocks resource, whose icon stands in for the "Blocks"
-    // word in the header stock and expand button (REQ-UI-BLOCKS-ICON).
-    const char* const kBlockItemId = "building_block";
-}
-
 const double HeaderBar::kSpeeds[]   = { 0.0, 0.5, 1.0, 2.0, 10.0 };
 const int    HeaderBar::kSpeedCount = 5;