ClangFormat: Fix UI issues

- 'Default' values remain so after save/load
 - the language is fixed to C++
 - the project settings are shown correctly
 - fix parsing configuration file
 - do not trigger slots when we fill the table

Change-Id: I91b477721b5084803324cd38d0cfeb9d5650dd9f
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangformat/clangformatutils.h

@@ -40,6 +40,9 @@ void createStyleFileIfNeeded(bool isGlobal);
 
 QString currentProjectUniqueId();
 
+std::string currentProjectConfigText();
+std::string currentGlobalConfigText();
+
 clang::format::FormatStyle currentProjectStyle();
 clang::format::FormatStyle currentGlobalStyle();