neovim: Reorganise directory layout

This also loads UltiSnips by setting a configuration option instead of
symlinking it to the default location.

users/simon/modules/default.nix

@@ -10,7 +10,7 @@
     ./misc.nix
     ./mpd.nix
     ./mpv
-    ./neovim.nix
+    ./neovim
     ./pass.nix
     ./programs.nix
     ./scripts.nix

users/simon/modules/neovim/default.nix

@@ -211,6 +211,7 @@ in
       {
         plugin = ultisnips;
         config = ''
+          let g:UltiSnipsSnippetDirectories = [ '${./UltiSnips}' ]
           let g:UltiSnipsExpandTrigger = '<tab>'
           let g:UltiSnipsJumpForwardTrigger = '<tab>'
           let g:UltiSnipsJumpBackwardTrigger = '<s-tab>'
@@ -302,10 +303,6 @@ in
     ];
   };
 
-  xdg.configFile = {
-    "nvim/UltiSnips".source = ../files/nvim/UltiSnips;
-  };
-
   home.sessionVariables.EDITOR = "nvim";
 
   home.packages = with pkgs; [