Slide legend to hide contigs by range

[qiyunzhu]

The sliding legends are convenient for re-scaling (re-setting the visual min/max) contigs. A potential new usage is to let the user slide the legends to show only contigs in the range. This is basically a shortcut to the "search" function".

To achieve this, one may add a button to the right of each legend. This button has "regular" and "pressed" status. When pressed, sliding the legend will trigger hiding instead of re-scaling.

This will also require modification of current selection / masking mechanism. Hiding contigs by sliding is easy and can be achieved using the current mechanism, but re-exposing hidden contigs by sliding isn't that easy. Something needs to be implemented to enable that.