fixed class reference
challenge show for comments
bug fix : it does not work, when raw_get is called with only entities.

for instance, Member.raw_get(["test user", "challenges"]) sends request with the url http://cs-api-sandbox.herokuapp.com/v1/members?testuser/challenges. because in raw_get method ["test user", "challenges"] is regarded as params, not entities.
implements '/account/challenges' page.
implements '/account/payment_info' page.
bug fix
layout work
implements '/account/invite_friends' page`
Merge branch 'cs-2047-port-payment-info'
Merge branch 'cs-2052-port-invite-members'
Merge commit 'e5be695705d149d6132873ffd4f395ba7cf6559c'

Conflicts:
	app/models/member.rb