Modifiers: add icon field to ModifierTypeInfo

With this change `outliner_draw.c` does not have to be
edited anymore when a new modifier is added.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D8998

source/blender/modifiers/intern/MOD_armature.c

@@ -281,6 +281,7 @@ ModifierTypeInfo modifierType_Armature = {
     /* type */ eModifierTypeType_OnlyDeform,
     /* flags */ eModifierTypeFlag_AcceptsCVs | eModifierTypeFlag_AcceptsVertexCosOnly |
         eModifierTypeFlag_SupportsEditmode,
+    /* icon */ ICON_MOD_ARMATURE,
 
     /* copyData */ copyData,