Merge branch 'statbox-any-label'

Add support for using any wxWindow (and not just the equivalent of
wxStaticText) as wxStaticBox label.

See https://github.com/wxWidgets/wxWidgets/pull/650

misc/schema/xrc_schema.rnc

@@ -1879,6 +1879,7 @@ wxStaticBoxSizer_horz =
         stdObjectNodeAttributes &
         stdSizerProperties &
         [xrc:p="important"] element label {_, t_text }* &
+        element windowlabel {windowNode}* &
         [xrc:p="o"] element orient  {_, "wxHORIZONTAL" }* &
         (wxBoxSizer_horz_item | objectRef)*
     }
@@ -1889,6 +1890,7 @@ wxStaticBoxSizer_vert =
         stdObjectNodeAttributes &
         stdSizerProperties &
         [xrc:p="important"] element label {_, t_text }* &
+        element windowlabel {windowNode}* &
         element orient {_, "wxVERTICAL" } &
         (wxBoxSizer_vert_item | objectRef)*
     }