add "add to fav" function on venue detail page - redirects to user home
.if venue+user already in user_fav table, it updates w/ new date
.if no date given, inserts into user_fav w/o date
.minor issue from above where it will display as 0000-00-00 (need to fix)
Merge pull request #34 from jennjwu/dev_jenn

add "add to fav" function on venue detail page - redirects to user home