Don't theme password-change template anymore, instead fork edx-platform

@jrbl (FYI: @caesar2164 @stvstnfrd)

I think we want to stop outright theming the password-reset-confirm template (the page on which you re-enter your new password).  This is because, by having an outright different file, we missed the changes that implemented the display of error messages in password complexity checking.

So I'd like to delete the themed version of this file and just fork the template in edx-platform.  See https://github.com/Stanford-Online/edx-platform/pull/88/files for the platform counterpart.