ARI: Add mailboxes resource for controlling and polling external MWI

Adds the following AMI commands:
PUT mailboxes/mailboxName
    modifies mailbox state and implicitly creates new mailboxes
GET mailboxes/mailboxName
    retrieves a JSON representation of a single mailbox if it exists
GET mailboxes
    retrieves a JSON array of all mailboxes
DELETE mailbox/mailboxName
    deletes a mailbox
Note that res_mwi_external must be loaded for these functions to
actually do anything.

Review: https://reviewboard.asterisk.org/r/3117/
........

Merged revisions 405553 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@405554 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/ari/ari_model_validators.h

@@ -498,6 +498,24 @@ int ast_ari_validate_device_state(struct ast_json *json);
  */
 ari_validator ast_ari_validate_device_state_fn(void);
 
+/*!
+ * \brief Validator for Mailbox.
+ *
+ * Represents the state of a mailbox.
+ *
+ * \param json JSON object to validate.
+ * \returns True (non-zero) if valid.
+ * \returns False (zero) if invalid.
+ */
+int ast_ari_validate_mailbox(struct ast_json *json);
+
+/*!
+ * \brief Function pointer to ast_ari_validate_mailbox().
+ *
+ * See \ref ast_ari_model_validators.h for more details.
+ */
+ari_validator ast_ari_validate_mailbox_fn(void);
+
 /*!
  * \brief Validator for ApplicationReplaced.
  *
@@ -1111,6 +1129,10 @@ ari_validator ast_ari_validate_application_fn(void);
  * DeviceState
  * - name: string (required)
  * - state: string (required)
+ * Mailbox
+ * - name: string (required)
+ * - new_messages: int (required)
+ * - old_messages: int (required)
  * ApplicationReplaced
  * - type: string (required)
  * - application: string (required)