Allow CHANGELOG to be viewable from the GUI

[TheWitness]

Describe the bug

There is no way to view the Cacti ChangeLog from the GUI

Expected behavior

There should be a location to access the Cacti ChangeLog from the GUI

Additional context

This issue is closely related to #3590 but will not go as far.

[netniV]

I've changed this from a bug to a feature, because it's not really a bug that you can't do it.