port hacker page form over to main registration form

[chen-ye]

not sure if we want to do this, given how close we are to closing registration. but for the sake of consistency, it might be something to do

[chen-ye]

@ariellebryn, would you be down for doing this? basically it involves getting rid of a whole bunch of our custom css rules and reimplementing validation and shit with the new integrated css.

[chen-ye]

the form layout itself is largely the same, except we changed plugins from select2 to selectize