Utils: Make aspect settings access implicit

Generally, aspects should use fromMap/toMap, but some older pages
use {from,to}Settings with always the same ICore::settings().

To make that less intrusive on the user code side, make that globally
implicit.

Task-number: QTCREATORBUG-29167
Change-Id: I29a8e23a31eb8061bb143e93931a07c6741eb7f9
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/coreplugin/dialogs/ioptionspage.cpp

@@ -6,8 +6,6 @@
 
 #include "ioptionspage.h"
 
-#include <coreplugin/icore.h>
-
 #include <utils/algorithm.h>
 #include <utils/aspects.h>
 #include <utils/layoutbuilder.h>
@@ -167,7 +165,7 @@ void IOptionsPage::apply()
         AspectContainer *container = m_settingsProvider();
         if (container->isDirty()) {
             container->apply();
-            container->writeSettings(ICore::settings());
+            container->writeSettings();
          }
     }
 }
@@ -323,9 +321,4 @@ PagedSettings::PagedSettings()
     setAutoApply(false);
 }
 
-void PagedSettings::readSettings()
-{
-    return AspectContainer::readSettings(Core::ICore::settings());
-}
-
 } // Core