ClangTools: Improve filtering

Replace the filter line edit in the toolbar by a tool button that pop
ups a dialog. In the dialog, the available checkers can be
selectd/unselected to filter the diagnostic view. Also, the diagnostic
view can be limited to diagnostics with fixits so that these can be
selected and applied as the next step.

For convience, add also some context menu entries to modify the filter
with regard to the current diagnostic.

Change-Id: Ifba3028805840658d72a39516c2b02da9864d4a6
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/clangtools/clangtoolsdiagnostic.h

@@ -54,6 +54,7 @@ class Diagnostic
 public:
     bool isValid() const;
 
+    QString name;
     QString description;
     QString category;
     QString type;