Fix slider

[yibeichan]

changes made

1. create slider based on minValue and maxValue rather than choices, the default setting is from 0 to 100
2. the current schema choices generation can remain it is now, we read choices["name"] for minLabel, midLabel, and maxLabel

looks like this

[yibeichan]

wait, my previous commits (from the isVis issue) are also here... i need to remove them

[yibeichan]

this branch messed up, i'm closing it and starting a new one