mc_pos_control_main smooth takeoff: enable position-xy/yaw control once above 0.5m from takeoff reference

just keep thrust vector pointing upward

smooth-takeoff. This is only required if someone writes a FlightTask where both position
and velocity setpoints are finite

made changes based on reviewer feedback. Also added a bool option for block_read and block_write PEC, as some devices may not use the PEC

    - libuavcan in PX4/Firmware (8958b42dada1e14f27c287a59b51ff26e90486a1): https://github.com/UAVCAN/libuavcan/commit/479d144ded9d5d16e234121ef9511b9ca9dfdac5
    - libuavcan current upstream: https://github.com/UAVCAN/libuavcan/commit/6174b8c10a2dbf47076ca7a7b5820a4c36c8a988
    - Changes: https://github.com/UAVCAN/libuavcan/compare/479d144ded9d5d16e234121ef9511b9ca9dfdac5...6174b8c10a2dbf47076ca7a7b5820a4c36c8a988

    6174b8c 2018-10-06 Pavel Kirienko - Link to the new forum

-Rearranged bus options to match other drivers
-Added TODO statement because driver cannot yet start on a specific external bus

- Added two external I2C bus options corresponding to newer Pixhawk hardware (px4fmu-v5)
- Switched from getopt to px4_getopt
- Fixed bus checking loop exiting early

    - sitl_gazebo in PX4/Firmware (31b110c2): https://github.com/PX4/sitl_gazebo/commit/70ca64654061fb7a4279846d9da1ad3512cfc6ba
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/d1f0bd4367d1cab01c772bb593a3f750b2f7dce2
    - Changes: https://github.com/PX4/sitl_gazebo/compare/70ca64654061fb7a4279846d9da1ad3512cfc6ba...d1f0bd4367d1cab01c772bb593a3f750b2f7dce2

    d1f0bd4 2018-10-10 Elia Tarasov - remove redundant check for gazebo major version greater than 7
a796798 2018-10-10 Elia Tarasov - change gazebo version for irlock plugin
83cadac 2018-10-10 Elia Tarasov - fix compile error for sonar plugin
aac3d20 2018-10-10 Elia Tarasov - fix compile error for lidar plugin
5a497ad 2018-10-10 Elia Tarasov - fix gps delay computation
3f0a769 2018-10-10 Elia Tarasov - fill timestamp inside plugin callback
779954c 2018-10-10 Elia Tarasov - send and recv sitl_gazebo message timestamp as unified type
46c4b29 2018-10-10 Elia Tarasov - proto: change timestamp name and type for consistency

 * The X-UAV Mini Talon airframe with the new type Plane V-Tail uses the new AAVVTWFF_vtail mixer.
The new mixer is derived from the AAVVTWFF mixer and is a generic V-Tail mixer. I left the flaps and wheel although there are no flaps and wheels on the mini talon to keep it generic. The airframe configuration is derived from the Albatross A-Tail.

vehicle state.

refactor use_obstacle_avoidance method

acceptance radius from the paramters and overwrite it if the mission item
has set acceptance radius