feat: Improved RangeWidget Styling

[ShrimpCryptid]

Resolves https://github.com/allen-cell-animated/agave/issues/103!

I'd recommending starting with the changes to RangeWidget.h and RangeWidget.cpp when reviewing.

• Renames properties of the RangeWidget to be more clear (minimum -> minBounds)
• Decoupled the first and second value sliders from min/max
  • This fixes a bug where the first/second sliders could be swapped, resulting in huge and incorrect ranges
• Updates styling for the slider handles based on requests from @TravisKroeker!
• Fixes visual bug where edges of sliders would get cut off
• Updates layouts where range sliders are used (sliders get a larger share of space than the labels)
• Fixed hovering behavior and coloration

Before: After:

Vertical:

Video Preview:

https://github.com/allen-cell-animated/agave/assets/30200665/6b01c522-69e3-457b-993f-91c2759b1742

Notes:

• The color is currently hard-coded for the track background, based on Travis' Figma design. Dan and I talked about how, ideally, this should be a style or theme color for platform compatibility reasons.