[horde] Cannot delete ingo rules

[Twilek]

> There should be a trash can icon to the left of the rule that you  
> can click on to delete it.

Curios: Same installation, same user:
Latest Firefox: No icons at all
Edge: "broken image" pictograms instead of icons
Chrome: "broken image"
Old IE: Icons show without problem

Other Icons of Ingo have the same problem. Icons in other Horde Apps  
don´t work as well, except Imp and Kronolith wich seem to work fine.

I am using the latest debian Apache2 and PHP 7.2...

The Chrome Console shows:
14 x "Refused to load the image 'data:image/png;base64,iVBO <...> '  
because it violates the following Content Security Policy directive:  
"default-src https: 'unsafe-eval' 'unsafe-inline'". Note that  
'img-src' was not explicitly set, so 'default-src' is used as a  
fallback."

So I guess it is my Content Security Settings with Apache that cause  
the problem. I have no idea why IE can still load the icons and why  
the icons of Imp and Kronolith are not affected.

As my security settings are not overly strict I guess other people  
might have that problem as well.

Regards

Henning