You can now bind a key-binding on mouse click to icons and buttons by setting
"action" property.
For example:
```css
icon-paste {
expand: false;
filename: "gtk-paste";
size: 24;
vertical-align: 0.5;
action: "kb-primary-paste";
}
```
Now it needs a configuration option to enable, this should be just part
of the theme now.
Sidebar is the "sidebar" widget.
If not set by theme, old behaviour is still followed.