OAuth provider support with functional demo/test.

Functional OAuth provider support including data storage of client/user tokens.
Documentation for the Credential object.
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documentation/schemas/Credential.markdown

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+Documentation
+=======================
+#### OpenPhoto, a photo service for the masses
+
+----------------------------------------
+
+### What's a Credential object for?
+
+The Credential object stores permissioning OAuth tokens granted by the user to various applications.
+
+Due to the distrubuted nature of the platform the model for applications and users is flattened and not relational. For every application there will be exactly 1 user.
+
+----------------------------------------
+
+### Schema for a User object
+
+    {
+      id: (string),
+      name: (string),
+      image: (string),
+      client_secret: (string),
+      user_token: (string),
+      user_secret: (string),
+      permissions: (set),
+      verifier: (string),
+      type: (enum),
+      status: (bool)
+    }
+
+----------------------------------------
+
+### Schema description
+
+  * id, A (quasi-)public token which identifies the application
+  * name, A human readable name describing the client
+  * image, The base64 encoded version of a 100x100 pixel image
+  * client_secret, A shared secret used to verify requests originated from the application
+  * user_token, A (quasi-)public token which idenfies the user
+  * user_secret, A shared secret to verify that the request originated from the application for the user
+  * permissions, A set of permissions the credential has (create, read, write, delete)
+  * verifier, A verification string to ensure that the `oauth_callback` parameter wasn't spoofed
+  * type, An enumerated field specifying the type of token (unauthorized_request, request, access)
+  * status, Numeric representation of the status (0=deleted, 1=active)