Fix IconButton image loading in Silica

Silica seems to support two different images for buttons,
one normal na done pressed-highlighted. For the pressed image,
it appends some stuff (highlight color) to the image url.
We don't need that (yet?) so it can be discarded.
Don't crash if the lsb_release utility is not installed

On some platforms, such as on Fedora 19 running on CubieBoard 2,
lsb_release is not installed. In such case, modRana should not crash
if it tries to run it and it is not there.