Option to change notifications behavirour

Problem/Motivation

Hi,

In some popular sites, notifications are done so that there are only number of new notifications, and
when clicking that, it goes to a notifications page.
When a site does not need the notifications to open in a "layer" but instead direct the user to the notifications page,
give option to direct user rom the notifications widget to user/*/notifications.

Steps to reproduce

Now if user has notifications, they appear when moving mouse over the notifications widget (the number of
unseen notifications)

Proposed resolution

Add in the DANSE settings page (/admin/config/system/danse) a new checkbox:

Link from the notifications widget to the notifications page.
(By default, the notifications in the notifications widget are displayed in a "overlay layer". Turn this on
to show only the amount of new notifications and make a link from it to notifications page.

Remaining tasks

User interface changes

API changes

Data model changes