Make it easy to exclusively render one data layer

[georgwiese]

Currently, multiple color layers have an opacity slider. What's rendered is a weighted sum of the two color layers. Sliders can be moved independently.

In our use case, where we have the raw data and the predictions as an RGB color layer, this doesn't really make sense, as can be seen here

I believe we should enforce that the sum of weights equals 1. I see two options:

• When sliding one slider, automatically adjust the others.
• Fix the ordering of color layers, then implement a behavior as in Photoshop, where some layers are on top of others.

However, this solution might not work for fluorescence data where layers are mapped to different colors and then are added with weight 1. Not sure how to solve this.

[philippotto]

We discussed that the actual use case of the issue is to quickly toggle the visibilities between layers. We agreed on using ctrl+click-on-visibility-check to make the clicked layer exclusively visible.