Support browsing solutions while frozen

[luxaritas]

Describe your idea

You should be able to use the "previous solution"/"next solution" buttons to browse through solutions while "freeze mode" (disabling computations) is active

Motivation

Eg, you may want to just flick through designs to get an overview of what they look like in target mode, even if they don't have available natural mode structures, but don't want to wait for each one to compute

Proposed Solution

The biggest challenge is that there is a mix of potential data available for each solution. It may have all computations cached, only some, or none. This can affect natural structure, metrics (eg, specbox), constraints, etc.

We should be able to show what information we do have available, while marking areas we don't have data as unavailable

Other Information

The previous "broken" implementation of this was disabled in #811 (more details there)