add new default.js file for common code

As first steps, instead of several specific calls to
jQueryUI.accordion(), do one call in default.js and
make it class-specific. Add the required class to the
markup. Also, move comment enabling in the new file.

Delete several now obsolete JS files.
merge comments.js into default.js
move items/list to standardized way of non-JS styles
move JS file for login page, fix syntax (was partially PHP)
use external jquery-UI
move form polyfills in one, unconditionally loaded file
Merge branch 'simplify-js'