improve participate_count method
add unique key (event_id, user_id) to participants table
Merge pull request #8 from dnond/participate_in_event

Participate in event
add participants list to event detail page
add participated event list to event index
add leader event list to event index page
improve user info page
improve time in view
fix error message
add footer view
add logout link to event index
improve login/logout link
improve participating event list on event index
improve showing canceled event in event detail page