Merge pull request #23 from meoooh/master

댓글기능 구현 완료.
거래 사진 업로드하
Merge commit 'd1517ee5a1813128a87056b39c36fea7e3f21963'

# By han
# Via ROR Lab. (1) and han (1)
* commit 'd1517ee5a1813128a87056b39c36fea7e3f21963':
  댓글기능 구현 완료.

Conflicts:
	app/models/bookkeeping.rb

해결함.
ProofSerializer 모델에 picture_url 이미지 types 추가함
add_proof return proof object
Merge pull request #24 from meoooh/master

before_filter :authenticate_user! 추가
Merge pull request #25 from subicura/master

add_proof return proof object