Vcs: Move static functions out of VcsPlugin "namespace"

Plan is to split VcsPlugin in the pure IPlugin and a new class
the remaining non-IPlugin bits of VcsPlugin, call it VcsPluginPrivate
and use that d-ptr for VcsPlugin. VcsPlugin-derived classes can
then use VcsPluginPrivate derived private, later pointer members
of the *Privates can be made proper members, moving towards the
otherwise predominant plugin setup pattern.

Change-Id: I62db9269e8ca50633c24b6d1d735d59c8fa8e5a5
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitplugin.cpp

@@ -1025,7 +1025,7 @@ IEditor *GitPlugin::openSubmitEditor(const QString &fileName, const CommitData &
     }
     IDocument *document = submitEditor->document();
     document->setPreferredDisplayName(title);
-    VcsBasePlugin::setSource(document, m_submitRepository);
+    VcsBase::setSource(document, m_submitRepository);
     return editor;
 }