Alternative IMP Background Selection (gamedir)

[kitty624]

• added two new options in ja2options.ini

• added new category, "Backgrounds", in INIEditorJA2Options.xml and ja2options.ini

• added new tag, in backgrounds.xml

• added information about new options into backgrounds.xml

• added new backgrounds for the new options into backgrounds.xml

• also added tags needed for disease feature to medical staff in merc backgrounds

this change is accompanying the relevant change in source