SPIKE: Pushable/combine with 0 thresholds

[polizz]

This is basically a feature request with some POC code to get your thoughts.

We use your control in the Range mode with multiple initial default values. We like pushable, but prefer not to have the threshold between handles. In this way, we want to allow the handles to collide, so that the handles you run into, push when they are run into, not before. Thus, you would go from two (or more) values to a single value when you collide with the other handle.

From what I can tell from your implementation, the handles are simply visualizations of an underlying array of (presumed) unique values, so this test currently behaves as though it combines the handles and you cannot select the other handle again. Without another widget to split them or reset the control state, I'm guessing there is no way to go back to your previous multiple handles.

[coveralls]

Coverage decreased (-0.4%) to 61.373% when pulling e19deeb2eab6194eed9f876ee06810541242dc3f on polizz:master into 0a07adac3694f5881ecf9dffcd4831ba6fafeff9 on react-component:master.

[coveralls]

Coverage decreased (-0.4%) to 61.373% when pulling 2aece15aedc27a0242a29737efb2162b693c2915 on polizz:master into 0a07adac3694f5881ecf9dffcd4831ba6fafeff9 on react-component:master.

[yoyo837]

Rebase please.