Make driving limbs easier

[i-make-robots]

• [x] Add a button that sets the target to the current end effector position.
• [x] Use the Dial class to bring back the easy FK driving of v2.
• [ ] Use the Dial class to bring back the easy IK driving of v2.

[i-make-robots]

278fa7c7c0efe94024e04fc44175ca537afc42ac Add a button that sets the target to the current end effector position.

[i-make-robots]

1. Target is somewhere in the scene.
2. Select MarlinRobotArm > Target to EE > Move
3. Target now at same pose as EE.

[i-make-robots]

Added FK dials.

[i-make-robots]

67cbda979a7e55b114fc01385fa7b965e1482c09

Made the motors section collapsible.

Put a named border on the FK dials.

[i-make-robots]

I don't see a good way to do IK from a panel that isn't just a crappy version of the existing "move target and set lin vel > 0."