[IMP] base, *: use a many2one for the company report layout

Before this rev. one could set the report layout on the company using a
hardcoded list (background, clean, standard, etc.). Other modules (typically
accounting modules) could add options in this list. The used template was built
on the layout key.

Now, the layout is a many2one field to a newly created model `report.layout`,
which is linked to a view with the layout architecture.

This gives more control to customize reports and create a new layout (without
creating a python module that extend the layout selection).

addons/web/static/src/js/fields/basic_fields.js

@@ -2826,56 +2826,6 @@ var AceEditor = DebouncedField.extend({
     },
 });
 
-var ImageSelection = AbstractField.extend({
-    supportedFieldTypes: ['selection'],
-    events: _.extend({}, AbstractField.prototype.events, {
-        'click img': '_onImgClicked',
-    }),
-
-    //--------------------------------------------------------------------------
-    // Private
-    //--------------------------------------------------------------------------
-
-    /**
-     * @override
-     * @private
-     */
-    _render: function () {
-        var self = this;
-        this.$el.empty();
-        _.each(this.nodeOptions, function (val, key) {
-            var $container = $('<div>').addClass('col-3 text-center');
-            var $img = $('<img>')
-                .addClass('img img-fluid img-thumbnail ml16')
-                .toggleClass('btn-info', key === self.value)
-                .attr('src', val.image_link)
-                .data('key', key);
-            $container.append($img);
-            if (val.preview_link) {
-                var $previewLink = $('<a>')
-                    .text('Preview')
-                    .attr('href', val.preview_link)
-                    .attr('target', '_blank');
-                $container.append($previewLink);
-            }
-            self.$el.append($container);
-        });
-    },
-
-    //--------------------------------------------------------------------------
-    // Handlers
-    //--------------------------------------------------------------------------
-
-    /**
-     * @override
-     * @private
-     * @param {MouseEvent} event
-     */
-    _onImgClicked: function (event) {
-        this._setValue($(event.currentTarget).data('key'));
-    },
-});
-
 return {
     TranslatableFieldMixin: TranslatableFieldMixin,
     DebouncedField: DebouncedField,
@@ -2906,7 +2856,6 @@ return {
     HandleWidget: HandleWidget,
     InputField: InputField,
     AttachmentImage: AttachmentImage,
-    ImageSelection: ImageSelection,
     LabelSelection: LabelSelection,
     StateSelectionWidget: StateSelectionWidget,
     FavoriteWidget: FavoriteWidget,