The button/action components in qqc2 are a little bit different than in qqc1. As a preparation for a full move to qqc2, implement a custom ToolButton component
reasons:
-overwrite the action upon pressing space, which makes https://bugs.kde.org/show_bug.cgi?id=392989 possible
-implements tooltips
-qqc2 buttons always display icon and text if specified (they do not seem to honor the display property)
all ToolButtons will be switched to this new component in a following patch