solo-1.2.3

diff from solo-1.2.2:

• motor slew rate limiter for current limiting
• new rate tune
• does not run motor recovery routine
• compiled with gcc-arm-none-eabi 4.9
• does not allow GCS mode changes during RC failsafe
• 2.5m minimum RTL climb within the cone
• sends target angle in MOUNT_STATUS instead of estimated angle