first step to the big video

missing:
- thumb
- refactor js code
Merge branch 'master' of https://github.com/catarse/catarse into channel-big-video
adjusts spacing
small readability improvement in application policy
Added contribution policy
style adjusts [Fix #59244802]
added after_action to verify if index is policy scoped
renamed only_admin to is_admin?
last fix on admin posts
instance @channel does not exists anymore instead we use channel helper [Fix #65495298]
added Scope to contribution policy and migrated users/contributions_controller to pundit.
fixed %s/policy_scoped/policy_scope/ and %s/verify_scoped/verify_policy_scoped/
created different policy for create and new in contribution. Project must be online, so we can move old logic from controller into policy.
Migrate projects/contributions_controller to pundit
removed contribution authorizations
implemented permitted_attributes for contributions
fixed problem with request_refund and new policy
need to use contributions table and not the backers [Fix #65491192]
animation tests
Merge branch 'master' of https://github.com/catarse/catarse into channel-text-changes