Suggestion : to add ` button - an alternative key for label 0

[GelionLin]

For the keyboard without ten-key pad, the first two labels 0 and 1 are too far away. This alternative key for label 0 could make the label keys to be connected to each other in sequence.

The simplest way is too add the following code on line after 927

if (pressed_key == '') current_obj_id = 0;`

Any thought?