Output notes bar

The next version will feature an Output Notes bar. Unlike the piano dialog, it doesn't accept user input; its only purpose is to show the output notes. It has the following features:

• dockable bar
• changes to vertical orientation automatically, depending on aspect ratio
• supports filtering by port and/or channel
• metronome notes are filtered out separately (this behavior is optional)
• piano size is selectable: 49, 61, 76, 88, or 128 keys
• optional key labels showing MIDI note names
• handles multiple instances of the same note, e.g. from different ports/channels
• handles bar being shown while notes are active, no dropouts