Small changes for UI

"Select all/none" is no longer a checkbox but a link. Also get rid of < li> tags because it feels redundant with checkboxes. 
The "add a bill" panel could now display 7 members without scrollbars. Given ihatemoney.org stats, more than 90% of projects have 7 members or less so scrollbars will be quite rare.
Design inspiration : http://37signals.com/svn/posts/3148-design-decisions-calendar-notifications