File model and api is almost complete

- Added "Kind" field to File model
- Added file query
- Added editFile mutation
- Added removeFile mutation

schema/root.graphql

@@ -22,6 +22,10 @@ type Query {
   posts(ids: [String!]!): [Post!]!
 
 
+  # Find file by ID
+  file(id: String!): File
+
+
   # Find current session
   session: Session!
 }
@@ -67,6 +71,13 @@ type Mutation {
   removePost(id: String!): Post!
 
 
+  # Edit a file
+  editFile(input: EditFileInput!): File!
+
+  # Remove a file
+  removeFile(id: String!): File
+
+
   # Log in
   login(username: String!, password: String!): Session!