Vcs: Merge IVersionControl and VcsBasePlugin hierarchies

They were 1:1 in parallel, with quite a bit of function call
ping-pong inbetween, for code-sharing-by-inheritance. Merge
them by making VcsBasePlugin inherit IVersionControl and
merge the derived classes below.

Size of this patch is hard to avoid as all seven systems have to
move simultaneously. Non-necessary potential follow-up cleanup
have been left out on purpose.

Change-Id: Icb71e4182af3db21069cc637e7ae87ffa3829791
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gerrit/gerritplugin.cpp

@@ -32,7 +32,6 @@
 
 #include "../gitplugin.h"
 #include "../gitclient.h"
-#include "../gitversioncontrol.h"
 #include "../gitconstants.h"
 #include <vcsbase/vcsbaseconstants.h>
 #include <vcsbase/vcsbaseeditor.h>
@@ -473,7 +472,7 @@ void GerritPlugin::fetch(const QSharedPointer<GerritChange> &change, int mode)
 // Try to find a matching repository for a project by asking the VcsManager.
 QString GerritPlugin::findLocalRepository(QString project, const QString &branch) const
 {
-    const QStringList gitRepositories = VcsManager::repositories(GitPluginPrivate::instance()->gitVersionControl());
+    const QStringList gitRepositories = VcsManager::repositories(GitPluginPrivate::instance());
     // Determine key (file name) to look for (qt/qtbase->'qtbase').
     const int slashPos = project.lastIndexOf('/');
     if (slashPos != -1)