Bind gO -> imenu

In Neovim, gO is bound to "open outline for current buffer". Emacs'
analogue for this is imenu. Plus, evil has no default keybind for gO.

modules/editor/evil/config.el

@@ -473,6 +473,7 @@ directives. By default, this only recognizes C directives.")
       :v  "gp"    #'+evil/alt-paste
       :nv "g@"    #'+evil:apply-macro
       :nv "gc"    #'evilnc-comment-operator
+      :nv "gO"    #'imenu
       :nv "gx"    #'evil-exchange
       :nv "gy"    #'+evil:yank-unindented
       :n  "g="    #'evil-numbers/inc-at-pt