added image_uploader via carrierwave
customise the avatar with default and thumb size
added default avatar image
migration and added column avatar
display avatar thumb at user menu
added the function of add new avatar and edit avatar
added the function of add new avatar and edit avatar
Fixed #15
Merge branch 'master' of github.com:hlee/books-share
Merge pull request #67 from hlee/master

added avatar to user
Fixed #65