Added new logged events

Added events to the graphing window to show flight mode changes.

Can use a custom build of betaflight v2.6.1. that logs.

• Current pitch/roll/yaw rates, expo and super expo factors.
• In the Viewer Legend there is a new button 'Log Setup' that can be used to display the logged rates.
• Flight mode change events on the timeline; so you can see exactly when you switched to SuperExpo or even turned on your beeper.
  Should still work fine on logs without the betaflight enhancements.