Allow hiding of UI elements to make player more minimal

  • Allow the user to hide these individual elements of the UI:

    • Playlist controls (buttons and search box), ie. the whole "row"
    • Player controls (back/pause/stop/next buttons)
    • Application Menu items


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    ...and after...
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    Additional context

    • Playlist controls are not useful to all users and these users may always live in a single playlist which is just the currently active window and it's playlist contents.
    • The Analyzer itself can currently be hidden from the UI and taking this a step further to hide the control buttons would free even more space up from the UI.
    • App menu items are hideable in a lot of Linux apps via the Alt+M keyboard combination. It would benefit Strawberry to also allow this part of the UI to be displayed or not. The keyboard combination to control this could be user configurable with a default as with other keyboard combinations.