Improve tool bar accesibility

[RafaelLinux]

For me at least, it's very difficult to distinguish actual icons (as you can see on picture) using KDE Plasma dark theme. I think that to have another icon set more legible it's necessary, with higher contrast and without that 3D like bottom on each of them. LibreOffice or GIMP have some dark theme icons very readable. I think that's the way IMHO

GIMP alternative icons ...

LibreOffice alternative icons ....