[feature] Send Group Notification / report builder

**Version and OS**
0.54.1 docker

**Is your feature request related to a problem? Please describe.**
If you know whatever you have set to watch changes every week, getting a group notification such as email would be easier then getting 12 emails.

I have it setup as;

```
{{watch_title}}
New Price: {{restock.price}}
Old Price: {{restock.original_price}}
```

**Describe the solution you'd like**
Under notifications page, have an option "send group notification" this option will make sure the notification is sent after all items from the group has been checked or a set time. If you have the check to happen each Monday at 7am and this check takes 5 minutes, the user could set the notification to send at 7:15am.

New option could be;

{{notification_group}} that could act like:

{{watch_title}}
{{restock.price}}

{{watch_title}}
{{restock.price}}

{{watch_title}}
{{restock.price}}

{{watch_title}}
{{restock.price}}

{{watch_title}}
{{restock.price}}

The output of this would be

Title 1
$5.99

Title 2
$33.99

Also under the info page you should add the version number and maybe total number of items/items to be processed.

Start at the notifications page and trace how watched items are checked and notifications are sent. Define how a group is identified, when its collected results are delivered, how {{notification_group}} is rendered, and what version and item counts appear on the info page; done means the grouped output and scheduling behavior are specified and working.

Written by the indexing model from the issue text.