use non-breaking space for button with no description

to preserve button's size

reverses some inappropriate replacements of .html with .text.

closes #5113

IPython/html/static/notebook/js/widgets/widget_bool.js

@@ -103,7 +103,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager){
 
                 var description = this.model.get('description');
                 if (description.length === 0) {
-                    this.$el.text(' '); // Preserve button height
+                    this.$el.html(" "); // Preserve button height
                 } else {
                     this.$el.text(description);
                 }

IPython/html/static/notebook/js/widgets/widget_button.js

@@ -32,7 +32,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager){
             // changed by another view or by a state update from the back-end.
             var description = this.model.get('description');
             if (description.length === 0) {
-                this.$el.text(' '); // Preserve button height
+                this.$el.html(" "); // Preserve button height
             } else {
                 this.$el.text(description);
             }

IPython/html/static/notebook/js/widgets/widget_container.js

@@ -137,7 +137,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager) {
                 });
             this.$title = $('<div />')
                 .addClass('widget-modal-title')
-                .text(' ')
+                .html("&nbsp;")
                 .appendTo(this.$title_bar);
             this.$body = $('<div />')
                 .addClass('modal-body')
@@ -147,7 +147,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager) {
                 .appendTo(this.$window);
             
             this.$show_button = $('<button />')
-                .text(' ')
+                .html("&nbsp;")
                 .addClass('btn btn-info widget-modal-show')
                 .appendTo(this.$el)
                 .click(function(){
@@ -237,14 +237,14 @@ define(["notebook/js/widgets/widget"], function(WidgetManager) {
             // changed by another view or by a state update from the back-end.
             var description = this.model.get('description');
             if (description.length === 0) {
-                this.$title.text(' '); // Preserve title height
+                this.$title.html("&nbsp;"); // Preserve title height
             } else {
                 this.$title.text(description);
             }
             
             var button_text = this.model.get('button_text');
             if (button_text.length === 0) {
-                this.$show_button.text(' '); // Preserve button height
+                this.$show_button.html("&nbsp;"); // Preserve button height
             } else {
                 this.$show_button.text(button_text);
             }

IPython/html/static/notebook/js/widgets/widget_selection.js

@@ -33,7 +33,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager){
             this.$droplabel = $('<button />')
                 .addClass('btn')
                 .addClass('widget-combo-btn')
-                .text(' ')
+                .html("&nbsp;")
                 .appendTo(this.$buttongroup);
             this.$dropbutton = $('<button />')
                 .addClass('btn')
@@ -59,7 +59,7 @@ define(["notebook/js/widgets/widget"], function(WidgetManager){
             if (options === undefined || options.updated_view != this) {
                 var selected_item_text = this.model.get('value_name');
                 if (selected_item_text.length === 0) {
-                    this.$droplabel.text(' ');
+                    this.$droplabel.html("&nbsp;");
                 } else {
                     this.$droplabel.text(selected_item_text);
                 }