[TASK] Image: `th` class added for image displayed in RevealModal
[TASK] Image: `th` class added for image displayed in RevealModal

That's cosmetic change (and follow up after
2b40615c87146f12135ed27bbd3c446603229c1a):  the image looks better
with it and we can re-use Foundation class to achieve that.

Relates: #6

million12/M12.Foundation,million12/M12.Foundation