add a visual indicator of the object's origin when displaying a Bracket

[sdumetz]

The changes are pretty much self-explanatory : Add an axis helper on the "Bracket" showing the selected object's bound to indicate it's transform origin.

This would help communicate the difference between Pose/Position (move relative to transform origin) and Settings/Transform (move the pivot point)

In the future, this "AxesHelper" could be extended to provide "handles" to move the object in the 3D space. For the moment it's just a visual helper.

The styling is THREE's default helper, I found it more readable than an all-yellow helper but other color choices are obviously possible.

[sdumetz]

Looks like I have a bug here where the Bracket disappear during loading when used as a blue placeholder.

I'll have to work this out.