Add Beat Preview to PatternClipView

[regulus79]

This PR changes the way PatternClips are drawn in include a simple "beat preivew," where each note in any non-empty instrument tracks within the pattern are drawn as 1/16 long rectangles on the ClipView. SampleClips and AutomationClips within patterns are not currently supported.

Note

I am not currently satisfied with the state of the visualization; perhaps some of you may have ideas on how to make it better, and/or if it should be optional (perhaps the solid color clips could be appealing to some)

Demo

pattern_clip_view_beat_preview_demo.mp4

(why is github thinking this is an audio file?)

Todo

• Fix clip view not updating when note velocity changes
• Add SampleClip support (likely going to be adding a single note rectangle at the sample startoffset)
• Add AutomationClip support (or not)
• Fix graphical bug of horizontal line of empty pixels
• Fix the drawing of notes to be between the clip highlight, otherwise the notes near the top and bottom botder will be slightly hidden.