v0.3.0

This month is all about visualizing data:

• Add functionality to plot JSON data
• Add chart panel, containing multiple plots (bottom panel)
• Chart panel and settings will be restored on restart
• Charts can be paused
• Panels can be hidden/overlap others completely
• Plot range can be customized
• Plot interpolation can be customized
• Migrated public broker from iot.eclipse.org to mqtt.eclipse.org
• Fix unrounded time intervals in the message history
• Fix weird plot curve interpolations