Add a refresh/randomize button in the preview panel

[Karl Goffin]

Current behaviour (optional)

Any time you open the configuration, a random Pokémon is displayed for the determinate & indeterminate progress bars.

Description of the desired feature (required)

A button to re-randomize these Pokémon without having to close & re-open the configuration

Why this feature would be valuable (optional)

Quality of life improvement, especially when playing with the paint types.

How to implement this feature (optional)

Add a refresh/randomize button

Additional information or context (optional)

This was brought up by @chylex in #59 as a possibility

[Karl Goffin]

added in 1.7.0