Enable switching to label/paint view later on in the workflow

[bnmajor]

The goal is to make it possible for users to be able to access labeling steps that are currently limited to the the setup UI in the active learning steps. The current goals are to offer an option to toggle the current "mode".

• Mode A would be the current active learning mode with the film strip
• Mode B would hide the film strip but show the labeling dialog to allow users to paint additional superpixels, rename categories, or change label colors.