Release candidate seven for v1.0.0 release

• This release candidate changes the default attitude and position estimator for all platforms to ekf_att_pos_estimator. From @Zefz.
• EKF offset fixes. From @sverling.
• Landing detector. From @Zefz.
• NuttX/ROS multi-platform improvements. From @thomasgubler.
• RAM optimizations. Brings FMUv1 back within limits (even when running two MAVLink links)
• Offboard / companion computer control: Support ACTUATOR_TARGET. From @matt-beall.
• Increase RTL descend altitude for fixed wing. From @AndreasAntener.
• PWM input driver. From @slayte via @tridge.
• Oreo led and smart battery drivers. From @rmackay9.
• Initial rover support from @mstuettgen
• mkblctrl improvements from @NosDE
• Offboard control fixes by @ziyangli
• Enforce one speed per I2C bus