Interface for connection related types

[MrOrz]

• Create Node, Edge, PageInfo and Connection interfaces and have similar object types inherit from them.
  • This helps components like <LoadMore> in rumors-site to create object-agnostic fragments that only retrieves common fields
  • Also defines more strict NonNull and ID so that their type is more rigorous.
  • When resolveEdge errors, the whole request (like ListArticle) would return null now, rather than return partially in the past. This makes more sense in terms of param error.
• Upgrade graphql-js to get better error message regarding interfaces. see graphql/graphql-js#2513

[coveralls]

Coverage increased (+0.04%) to 88.706% when pulling c12f235dce9715d1fab4b3df5300feab164748f9 on interfaces-non-null into 869bfcb4f24791793781f9a89d546d830e614fad on master.