Vcs: Move handling of settings from VcsBaseClient to VcsBaseClientImpl

... and update users of that functionality accordingly.

Unexpected plus: Now every supported VCS actually saves their setting
when requested.

Change-Id: I02db7b2ce14e5f52d26409b2a01aea290c2a294a
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitversioncontrol.h

@@ -66,7 +66,6 @@ public:
 
     void emitFilesChanged(const QStringList &);
     void emitRepositoryChanged(const QString &);
-    void emitConfigurationChanged();
 
 private:
     GitClient *m_client;