Update cell widget for molecule

[superstar54]

In step 1, we always show the cell parameters: a, b, c, etc, even for molecular systems, this is not consistent.

[AndresOrtegaGuerrero]

Well, this part we do need to know what is the cell we are using , even if the user want to have some control of how big is the cell. or even to know if the coordinates are inside the box. But this is a change of aiilab-widget base for periodicity none (molecule) no in qe app.