introjs background now darker for easier reading
Fixed app menu's position
New zoom system

No more need for screen resolution or screen diagonal input.
Lockratio always on

The print size will always be proportional to the image width.
Refactored zoom

Zoom doesn't require screen resolution or diagonal anymore. All data for
performing zoom is now embedded in the html elt (using
data-previous-value).
step number now has dedicated data-attr for setup