Use sliders for numerical values and combine resolutions

[Carifio24]

This PR makes two primary changes to the export dialogs:

• Use sliders rather than text fields for numerical values. For now we set integer values to have a range of [1, 100], and floats to have a range of [0.01, 1] with a precision of 0.01. This works well for all of the quantities that we currently have (floats are used only for opacities at the moment), but if that's not the case later we can revisit.
• Per a suggestion from Michelle, combine theta and phi resolutions for scatter spheres into just "resolution" at the user dialog level. Internally all of our functions still support making theta and phi resolutions different.