Extend backend-agnostic vc functionality

this commit adds a default keybinding for the vc-gutter hydra (leader-g
.) if both vc-gutter and hydra are enabled. It ensures that the various
vc-*-log-view-modes open up in emacs state, and it adds hg, svn and bzr
to the list of vc backends handled by git-gutter

modules/ui/vc-gutter/config.el

@@ -51,6 +51,7 @@ is deferred until the file is saved. Respects `git-gutter:disabled-modes'."
               (git-gutter-mode +1)
               (remove-hook 'after-save-hook #'+vc-gutter-init-maybe-h 'local)))))))
 
+  (setq git-gutter:handled-backends '(git hg svn bzr))
   ;; Disable in Org mode, as per
   ;; <https://github.com/syl20bnr/spacemacs/issues/10555> and
   ;; <https://github.com/syohex/emacs-git-gutter/issues/24>. Apparently, the