beatracker: Provide a mechanism for listing all beatracker phrases

[oubiwann]

The listing will display:

• [ ] index number
• [ ] name (if set)
• [ ] current state: playing, paused
• [ ] start beat (absolute)
• [ ] repeated? (boolean)
• [ ] end beat
• [ ] beat length

Depends on:

• 20

• 22

• 25

Part of:

• 19