Show incompatible kits in Add Kit

And implement a tooltip for them

Task-number: QTCREATORBUG-7870
Change-Id: I4975dd24ca2b619ebcbd0393f97311590ed4930f
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/projectexplorer/project.cpp

@@ -243,9 +243,10 @@ Target *Project::target(Kit *k) const
     return 0;
 }
 
-bool Project::supportsKit(Kit *k) const
+bool Project::supportsKit(Kit *k, QString *errorMessage) const
 {
     Q_UNUSED(k);
+    Q_UNUSED(errorMessage);
     return true;
 }