[mediacontroller] Use icon tabs to select player
Show the available players as an icon row of tabs instead of a combobox. The player name is shown in a tooltip on hover.
The selector is also moved into the applet's footer (in the first commit), for consistency and aesthetics, but also to be able to expand it with more media controls in a future (@broulik had some ideas)
| Combo in the footer | Icon tabs |
|---|---|
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