Vcs: Use PagedSettings for all plugin settings

Hopefully the last structural change for a while.

Settings lifetime is again tied to the plugin private.

Change-Id: I221e8b8baa69422306191b48a9f034ef5b1a0dc2
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/mercurial/mercurialplugin.cpp

@@ -169,8 +169,8 @@ private:
     void createRepositoryActions(const Core::Context &context);
 
     // Variables
+    MercurialSettings m_settings;
     MercurialClient m_client;
-    MercurialSettingsPage m_settingsPage;
 
     Core::CommandLocator *m_commandLocator = nullptr;
     Core::ActionContainer *m_mercurialContainer = nullptr;