Eeschema: Fix a very old bug relative to the tool to load power parts:

Previously, only the lib named "power" was used (and therefore power parts defined in other libs not shown).
Now, all power parts can be loaded from any library.
Also, when loading power parts from the chose component dialog or the lib viewer, libs and parts are filtered:  only power parts and libs containing power parts are listed.
Hotkeys: move a few global strings in the files where ther are actually used (and make them local.) and code cleaning.
Fix a few other minor issues.

common/basicframe.cpp

@@ -632,13 +632,6 @@ void EDA_BASE_FRAME::CopyVersionInfoToClipboard( wxCommandEvent&  event )
     tmp << wxT( "OFF\n" );
 #endif
 
-    tmp << wxT( "         KICAD_USE_WEBKIT=" );
-#ifdef KICAD_USE_WEBKIT
-    tmp << wxT( "ON\n" );
-#else
-    tmp << wxT( "OFF\n" );
-#endif
-
     wxMessageBox( tmp, _("Version Information (copied to the clipboard)") );
 
     wxTheClipboard->SetData( new wxTextDataObject( tmp ) );