How to "unlink" bone? I've been following along in a tutorial on animation and I must've inadvertently clicked on something because I've animated a part of the model that shouldn't be attached to a bone/armature. (Notice the double rectangles to the upper left of the robot head. These are part of the robot's head, and should remain fixed to the head, but instead they're animated along with the arms). 

How do I "unlink" the "head" element(s) in question so that they stay fixed? 

Also, I've now just gotten into a state where I can't select anything. The properties area is now all about armatures, and I can't see/recover the "normal" tool icons like "wrench" (for boolean operations, etc.) or "sphere" (for materials, etc.), so I can't do "normal" editing operations. 

Here is the file on GitHub: https://github.com/DragonForest/first-robot.

Thank you!
In Edit Mode, select the Bone and press W

You can switch the bone direction and others