Give feedback of the joint space exploration

[guilhermelawless]

Related issue: #54 as that is where this would make the most sense, but this can also apply to automatic and from-bag modes.

Since we have access to the URDF, that gives us knowledge of the joint limits. During a "pose capture" mode (#54) or even during calibration feedback could be given as to how much of that joint's available space has been explored already. You mentioned this as being critical in #17.

Ideas for feedback:

• Simple percentage of explored space
• A plot (histogram, violin) that shows the distribution of saved positions over the joint space.

[mikeferguson]

Also a good idea for inclusion in #51