Display playback head.

[vigliensoni]

Use two different colours:

• one when dragging
• one to mark the position of the playback head without dragging

[vigliensoni]

I have already implemented red head for position and green when moving.

For some reason, though, the position of the mouse doesn't get translated exactly to the position where the rectangle is being drawn.

• [x] Perhaps one of the canvas is smaller? This was the reason!

Another issue is the canvas is being overwritten all the time.

• [x] Perhaps another canvas on top of the previous one is needed?

• [x] Check why the playback head is rendered in a different position

• [x] Check how to retrieve point and render in the overlay layer, while rendering the latent space in the other one

• [x] decide if include button to delete trajectories, or not displaying the trajectories

[vigliensoni]

Fixed in 632f928dfdc5c306ee183c7ba803f5d411e46404