KitInformation: Make validate work on const Kits and add fix method

Make sure validate will not modify kits, add a fix method to do that
when kits are loaded/added.

Change-Id: Ib378af0f3470b2caf64177b35fca061089ac4523
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/projectexplorer/kit.cpp

@@ -151,7 +151,7 @@ bool Kit::isValid() const
     return d->m_id.isValid() && d->m_isValid;
 }
 
-QList<Task> Kit::validate()
+QList<Task> Kit::validate() const
 {
     QList<Task> result;
     QList<KitInformation *> infoList = KitManager::instance()->kitInformation();