solo-1.2.11

diff from solo-1.2.9:

• removes air density compensation that was causing issues during high-elevation flight
• prevent large rotation rates from causing the magnetometer reset to fail
• add MAV_CMD_SOLO_BTN_PAUSE_CLICK to de-race the PAUSE button
• loosens yaw again - flight test resulted in some disturbances getting through
• fix dataflash log deletion so that it correctly finds the oldest log after wraparound
• new shutdown sound!