Add hit testing clarification to schematic library editor.

* Create library collector class.
* Add clarification menu to library editor when multiple items are found
  at the current position.
* Add get clarification menu text to all objects derived from LIB_ITEM.
* Add get menu bitmap for all objects derived from LIB_ITEM.
* Improve LIB_PIN bounding box calculation.
* Rename LIB_ITEM::DoGenCopy to doClone to match behavior defined in base
  class EDA_ITEM.
* Minor class renaming for improved code consistency.
* Added less than operator to EDA_ITEM.

common/base_struct.cpp

@@ -81,7 +81,6 @@ EDA_ITEM* EDA_ITEM::doClone() const
 }
 
 
-// see base_struct.h
 SEARCH_RESULT EDA_ITEM::IterateForward( EDA_ITEM*     listStart,
                                         INSPECTOR*    inspector,
                                         const void*   testData,
@@ -135,6 +134,15 @@ wxString EDA_ITEM::GetSelectMenuText() const
 }
 
 
+bool EDA_ITEM::operator<( const EDA_ITEM& aItem ) const
+{
+    wxFAIL_MSG( wxString::Format( wxT( "Less than operator not defined for item type %s." ),
+                                  GetChars( GetClass() ) ) );
+
+    return false;
+}
+
+
 #if defined(DEBUG)