Lima: Export cur roi in settings

Closes #3840 (closed) #3836 (closed)

The source of truth for the Lima image ROI is BLISS.

This value was not synchronized between session.

This PR store this ROI in the settings in order to share the save value with the other sessions.

Plus 2 small clean up

• Returns None instead of an implicit None
• Drop of fallback for Lima tango API image_width/image_height (and only use image_max_dim)

I also would like this change to be backported to BLISS 1.11.x