Hide breakpoints when in a RBL session

[DonJayamanne]

• Use run by line
• Add 2 break points
• Hit the Continue button, and it will run to completion without stopping at the break points

Identified when @DavidKutu was demoing the Continue feature.

[DavidKutu]

This is intended, the button is meant to exit RBL mode and execute the cell normally.

[greazer]

We need to finalize the UI coordination between RBL and notebook debugging.

[DavidKutu]

We decided on hiding the breakpoints while using RBL. Not removing them, as they need to persist. Just hide them.

[roblourens]

We could switch them to look like this, which is what unbound breakpoints look like

I suspect that they are actually being bound but then manually skipped over by RBL

[roblourens]

I think this is ok, haven't heard about confused users