Add new icons to Assembly work bench

Including new body icons for the treeview and
PartDesign create new body command.
Move all Assembly constrains icons into their
own sub directory of the icons directory
add "STEP, IGES or BREP" to the tool tip
of Assembly add existing Component command

src/Mod/Assembly/Gui/ViewProviderConstraintGroup.cpp

@@ -39,6 +39,7 @@ PROPERTY_SOURCE(AssemblyGui::ViewProviderConstraintGroup,Gui::ViewProviderDocume
 
 ViewProviderConstraintGroup::ViewProviderConstraintGroup()
 {
+  sPixmap = "Assembly_Assembly_Constraints_Tree.svg";
 }
 
 ViewProviderConstraintGroup::~ViewProviderConstraintGroup()