sliders should account for min/max values for calculating step/speed when dragging

[ngokevin]

Trying to drag geometry.thetaLength which can be 0 to 360. When I try to drag the value, the most I can do is like 5 degrees at a time.

Editor perhaps should know that the max is 360 to calculate how fast the slider should change the value.

[cvan]

We should use proper input[type=number] and input[type=range] (issue #29).