Made wxBORDER_THEME the same as wxBORDER_DEFAULT

Moved wxControl::GetBorderStyle into wxWindowMSW::GetBorderStyle
but added GetBorderStyle to have the same behaviour as before (so e.g.
notebook panels don't get borders)
Improved help window borders


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@47963 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/panelg.h

@@ -79,6 +79,8 @@ public:
     virtual bool IsCanvasWindow() const { return true; }
 #endif
 
+    // choose the default border for this window
+    virtual wxBorder GetDefaultBorder() const { return wxWindowBase::GetDefaultBorder(); }
 
     WX_DECLARE_CONTROL_CONTAINER();