Fix notification icon on (at least) SFOS 4.2

While I was testing things with my SFOS 3.4 Jolla Phone, I noticed that it had the correct notification icon, whereas my X10II at at SFOS 4.2 did not. This fixes the latter, and doesn't affect the former.

The remote action icon doesn't work as-is on my 4.2, but setting a full path in the field, I get the icon next to the to the message. When we eventually have avatar images, it can be simply dropped in place.