Full screen editing mode UI

[mneuschaefer]

Currently the full screen editing mode appears when you double click on an existing squarelet, but it is not apparent how to leave this state. How about this behaviour instead:

• With a double click, you can edit the square in its existing dimensions, while the rest of the canvas remains visible (similar to the mode when you create a new squarelet)
• In the editing mode, an "expand" button appears to the top right of the small squarelet
• when you click it, you get to the full screen editing mode for this square
• in the full screen editing mode, a button appears to the top right with the option to reduce the window size
• to leave the full screen editing mode (all changes saved automatically), you click the button top right, or somewhere outside the canvas

Some sketches how it could work:

[aivuk]

The problem is that the fullscreen mode was created because of the zoom feature. If you zoom out, we can't have the editor with the size of the square being edited, or it going to be very small. And we need to have a standard size for the ui interface and editor text size.