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/fossil/fossilplugin.cpp

@@ -187,10 +187,9 @@ public:
     bool pullOrPush(SyncMode mode);
 
     // Variables
+    FossilSettings m_settings;
     FossilClient m_client;
 
-    OptionsPage optionPage;
-
     VcsSubmitEditorFactory submitEditorFactory {
         submitEditorParameters,
         [] { return new CommitEditor; },