add dot-dsl exercise

[oxe-i]

This PR also adds a key "editor" in the config.json for resistor-color-trio, allowing Extra.lean to be seen by students in the online editor.

[oxe-i]

This exercise completes the macro "path" I had planned for the track. This means I think the exercises we have should already give students enough practice to reach a good level on the topic, and we don't need to add another one focused on that.

The next topic I'm going to focus on is proof.