Use wxTextProofOptions itself to enable or disable the checks

Remove a separate "bool enable" argument of EnableProofCheck() and use
wxTextProofOptions::IsSpellCheckingEnabled() to decide whether the
checks should be enabled or disabled.

Also remove wxTextProofOptions ctor and provide named static factory
functions for creating the objects of this class with clearly defined
meaning.

include/wx/gtk/textctrl.h

@@ -98,10 +98,8 @@ public:
 
 #if wxUSE_SPELLCHECK && defined(__WXGTK3__)
     // Use native spelling and grammar checking functions.
-    virtual bool EnableProofCheck(
-            bool enable = true,
-            const wxTextProofOptions& options = wxTextProofOptions()
-        ) wxOVERRIDE;
+    virtual bool EnableProofCheck(const wxTextProofOptions& options
+                                    = wxTextProofOptions::Default()) wxOVERRIDE;
     virtual bool IsProofCheckEnabled() const wxOVERRIDE;
 #endif // wxUSE_SPELLCHECK && __WXGTK3__