Gender field and bug fixes

models: Expanding the gender field to include M/F, Other, and
unspecified. Appropriate changes in user_registration_form
base.js: Modifying the screen size selection behavior to include
mobile, tablet, and full for use with equal-cols.js. Appropriate
changes to reflect the new size selection.
equal-cols: bug fixes to make sure the columns have the correct size
for the screen width.