feat(alerting): alert list fixes

public/app/features/alerting/alert_list_ctrl.ts

@@ -47,6 +47,7 @@ export class AlertListCtrl {
   openHowTo() {
     appEvents.emit('show-modal', {
       src: 'public/app/features/alerting/partials/alert_howto.html',
+      modalClass: 'confirm-modal',
       model: {}
     });
   }

public/app/features/alerting/partials/alert_howto.html

@@ -2,7 +2,7 @@
 	<div class="modal-header">
 		<h2 class="modal-header-title">
 			<i class="fa fa-info-circle"></i>
-			<span class="p-l-1">How to add an alert</span>
+			<span class="p-l-1">Adding an Alert</span>
 		</h2>
 
 		<a class="modal-header-close" ng-click="dismiss();">
@@ -12,7 +12,7 @@
 
 
 	<div class="modal-content">
-		<p class="p-a-2 text-center offset-lg-2 col-lg-8">
+		<p class="p-a-2 text-center offset-lg-1 col-lg-10">
 			Alerts are added and configured in the <strong>Alert Tab</strong> of any dashboard
 			graph panel, letting you build and visualize an alert using existing queries.
 			<br> <br>