add back button to subheader

frontend/app/proposal/create/subheader/most-proposal-list-subheader.pug

 extends /modules/subheader/responsive-subheader.pug
 
 block left
-  most-subheader-burger-button.hidden-md
-    i.mdi.mdi-menu
+  group-subheader-back-button
   span.title.ellipsis #{__('Tạo đề xuất')}

frontend/app/proposal/detail/subheader/most-proposal-detail-subheader.pug

 extends /modules/subheader/responsive-subheader.pug
 
 block left
-  most-subheader-burger-button.hidden-md
-    i.mdi.mdi-menu
+  most-subheader-back-button
   span.title.ellipsis {{::$ctrl.title}}
 
 block right

frontend/app/subheader/most-subheader-back-button.component.js

+(function(angular) {
+  'use strict';
+
+  angular.module('linagora.esn.most')
+
+  .component('mostSubheaderBackButton', {
+    templateUrl: '/linagora.esn.most/app/subheader/most-subheader-back-button.html'
+  });
+})(angular);

frontend/app/subheader/most-subheader-back-button.pug

+button.btn.btn-link.hidden-xs(href='', esn-back-button='most.proposal')
+  .flex-vertical-centered
+    i.mdi.mdi-arrow-left.mdi-margin-right
+    span #{__('Back')}
+button.btn.btn-link.btn-icon.visible-xs(href='', esn-back-button='most.proposal')
+  i.mdi.mdi-arrow-left