no need for Registry in plot_api/to_image

... and 'enforce' Registry in components/modebar/
    (like for all components really).

Author: etpinard

src/components/modebar/buttons.js

@@ -13,7 +13,6 @@ var Registry = require('../../registry');
 var Plots = require('../../plots/plots');
 var axisIds = require('../../plots/cartesian/axis_ids');
 var Lib = require('../../lib');
-var downloadImage = require('../../snapshot/download');
 var Icons = require('../../../build/ploticon');
 
 var _ = Lib._;
@@ -60,7 +59,7 @@ modeBarButtons.toImage = {
             format = 'svg';
         }
 
-        downloadImage(gd, {'format': format})
+        Registry.call('downloadImage', gd, {'format': format})
           .then(function(filename) {
               Lib.notifier(_(gd, 'Snapshot succeeded') + ' - ' + filename, 'long');
           })

src/plot_api/to_image.js

@@ -8,7 +8,7 @@
 
 'use strict';
 
-var Registry = require('../registry');
+var plotApi = require('./plot_api');
 var Lib = require('../lib');
 
 var helpers = require('../snapshot/helpers');
@@ -155,7 +155,7 @@ function toImage(gd, opts) {
             var width = clonedGd._fullLayout.width;
             var height = clonedGd._fullLayout.height;
 
-            Registry.call('purge', [clonedGd]);
+            plotApi.purge(clonedGd);
             document.body.removeChild(clonedGd);
 
             if(format === 'svg') {
@@ -196,7 +196,7 @@ function toImage(gd, opts) {
     }
 
     return new Promise(function(resolve, reject) {
-        Registry.call('plot', [clonedGd, data, layoutImage, configImage])
+        plotApi.plot(clonedGd, data, layoutImage, configImage)
             .then(redrawFunc)
             .then(wait)
             .then(convert)