Please, provide an easy way to use themable icons.

Use case: bubbles for AutoTest plugin (results pane) should be themable with the colours for the respective message type.

This avoids on the one hand the need to provide an icon for each message type and on the other one would have to provide icons for each QC theme which is currently not done at all (which leads to inconsistent colouring of the results pane when you compare the colour of the icon and the message type)