Describe the new feature or enhancement

After a frustrating meeting with the professor and a PhD student where we wanted to take a look a the evoked responses from our pilot data, here's a request:

Could we please make plot_evoked_topo more interactive in the following ways:

• Buttons / hotkeys for increasing/decreasing ylim
• Buttons / hotkeys for selecting only mags, grads, joining grads
• Legend present inside the new plots that open when you click on a channel

And a bug:

The default ylims for grads and mags are a bit off. The grads are too small.

Describe your proposed implementation

Added event handlers to the matplotlib figure generated by plot_evoked_topo.

Describe possible alternatives

change and re-run your code very time you want to change any of the above.

Additional context

No response