Multiple notifications are generated when navigating to future weeks/months

In order to reproduce the problem, go to Calendar.WebHome page and using the calendar navigation buttons (< and >), try to navigate to 5-6 weeks in the future.
This will cause the loading of each week's calendar as showed in calendarNotifications.png.

This is actually a Notifications Widget issue reported in XWIKI-18514. However, since that will be fixed in a later version (12.x, 13.x) and the minimal supported version of the Full Calendar macro is 7.4, a fix can be provided in the application.