Split apart debugger options pages, allow specifying a path to CDB.

Modify engine creation funcs to populate a list of option pages
to be able to handle engine enabling independently of the
actual engine creation.

src/plugins/debugger/debuggerplugin.h

@@ -56,8 +56,6 @@ namespace Internal {
 
 class DebuggerManager;
 class DebugMode;
-class GdbOptionPage;
-class DebuggingHelperOptionPage;
 class LocationMark;
 
 class DebuggerPlugin : public ExtensionSystem::IPlugin
@@ -108,9 +106,6 @@ private:
     DebuggerManager *m_manager;
     DebugMode *m_debugMode;
 
-    GdbOptionPage *m_generalOptionPage;
-    DebuggingHelperOptionPage *m_dumperOptionPage;
-
     QString m_previousMode;
     LocationMark *m_locationMark;
     int m_gdbRunningContext;