Median Arrow does not update with dynamic strings

[marlitas]

While working on #147 I noticed:

It seems this just requires another listener for when the bounds change. ManualConstraint might work here.

[matthew-blackman]

I can see two solutions to this:

1. In InfoValuesNode, put the median arrow in the same parent as dataValuesContainer and position it relative to its parent. This way when the dataValuesContainer is shifted the arrow will be as well.
2. Call update in InfoValuesNode if the dataValuesStringProperty changes.

Thoughts as to which of these would be better @marlitas, or if there is another way?

[marlitas]

We addressed this with ManualConstraint and it's working really well, however we didn't feel great about creating a class property for medianValueNodes. Would like for @samreid to review.

[samreid]

@matthew-blackman and I reviewed this, and it is really great. @matthew-blackman will apply the same strategy in another spot in another issue.

[matthew-blackman]

Closing and continuing data values work in #363