Pre-Roll and Auto Move Playhead

[maiko3tattun]

New Features:

• Auto Move Playhead: When notes are selected, the playhead moves to the position of the first note in the selection. This feature is disabled by default.
  
• Pre-roll: Playback starts a specified number of measures before the playhead’s current position. This feature is disabled by default; you can change the number of measures by right-clicking the button in the MainWindow.
  
  
• Both of these are common features in DAWs.

Internal Changes:

• The code that moves the playhead when playback stops has been moved from the ViewModel to the Model.
• A generic ComboBoxDialog has been added.

[maiko3tattun]

@nagotown This PR does not support negative timelines. The playhead is prevented from moving before 0.

[maiko3tattun]

Pre-roll is a feature that rewinds the playhead just before playback begins; depending on the DAW, it may also be referred to as a “count-in” or similar term.
video: https://discord.com/channels/551606189386104834/892242627032936469/1548228499637276784