So far our `IconButton` hasn't been a proper button control which comes
with many downsides, such as:
- Some default button behaviours need to be simulated (e.g. `onClicked`)
- Any support built-in features for all controls in QML like `ToolTip` aren't can't be used
- There are probably accessibility aspects to it as well
We use the `IconButton` in many different places. Sometimes it doesn't
even act as a button, but just as an icon. I suggest we introduce a separate
`StatusIcon` component for that in future changes.
This commit turns the `IconButton` into a proper `RoundButton`, restoring
the control behaviour and features we get from QML.
This also required to expose the `icon` property as a `iconImg`,
because a `RoundButton` already comes with an `icon`.
On the other hand, we could remove the `onClick` simulation and can now
take advantage of components like `ToolTip`.
f4d16d7661