central styles for forms
move comment preview styles to separate file
move markdown stylesheet to subfolder
centralize candidate and review list styles
split review styles for list and view
remove outdated admin menu styles
more central, reused styling
fix JS error
add separate JS file for form checking

Also enable form-checking in login.php.
remove old debug code from login.js
minor JS syntax fix
some JS polyfill changes

Add a general polyfill for autocomplete lists. Move
polyfills to a subfolder. Add a general loader script
for <form> polyfills. Only load scripts required by
the client (via Modernizr.load).