Fix the rounded hexagon shape of Badges in the mosaic

[aurelticot]

The current hexagon shape is created via a simple polygon clip path which doesn't have rounded corner.

This is fine when a badge has an image but it is not when that hexagon shape is filled with a background to create the "Show all" button or for the "no content" fallback, as we clearly see the corner.

We need to use a path instead of the polygon.