* Simplify TrackLabelButton
Remove the dependency to `Instrument` and `InstrumentTrack` from `TrackLabelButton`. The icon of an `InstrumentTrackView` is now determined in the class `InstrumentTrackView` itself using the new static method `determinePixmap`. This enables the removal of the overridden `paintEvent` method from `TrackLabelButton`.
It was also attempted to keep a non-static member function version and to use the `InstrumentTrackView`'s model with a cast. However, this did not work because 'setModel' is executed as the very last step in the constructor, i.e. the model is not already set when `determinePixmap` is called. Pulling it to the top is too risky right now.
* Add helper method isInCompactMode
Add the helper method `isInCompactMode` which knows how to use the `ConfigManager` to determine if the option for compact track buttons is enabled. This removes duplicate code with intricate knowledge of the keys under which compact mode is stored.
* Set song as modified when track name changes
Extend `Track::setName` to set the song as modified whenever the track name changes. This moves the update into a core class and enables the removal of the dependencies to `Engine` and `Song` from the GUI class `TrackLabelButton`.
Also add a check if the name is really changed and only perform the actions if that's the case.
To make this work the implementation of `setName` had to be moved from the header into the implementation file.
* Keep instrument and sample content at top on resize
Keep the content of the instrument and sample track at the top of the widget if the widget is resized. This is also fixes a bug where the `TrackLabelButton` does not react anymore when the size is increased.
Technically the layout with the actual widgets is put into another vertical layout with a spacer that consumes all remaining space at the bottom.
* Vertical track resizing via mouse wheel
Enable to vertically resize tracks using the mouse wheel. Scrolling the mouse wheel over the track view with the control key pressed will increase/decrease the height by one pixel per wheel event. Pressing the shift key will increase/decrease in steps of five pixels.
Extract code that can be shared between the existing and the new way to resize the track into the private helper method `resizeToHeight`.
* Render beat pattern step buttons at the top
Render the step buttons of beat patterns at the top instead of at the bottom so that they stay aligned with the other elements to the left of them (buttons, knobs, etc).
Set the y offset to 4 so that the step buttons are vertically aligned with the other elements. The previous calculation lead to a minimum offset of 6 which always made the step buttons look misaligned.
Introduce the new static variable `BeatStepButtonOffset` which ensures that the rendering and the evaluation of mouse clicks do not go out of sync.
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