ofono: add MessageManager and Message API.

ofono: add MessageManager and Message API.

This covers the usage we expect for our message application:
  - MessageManager:
     - SendMessage(): ofono_sms_send()
     - ServiceCenterAddress: ofono_service_center_address_get()
     - UseDeliveryReports: ofono_use_delivery_reports_get()
     - Bearer: ofono_message_bearer_get()
     - Alphabet: ofono_message_alphabet_get()
     - MessageAdded, MessageRemoved: ofono_sent_sms_changed_cb_add()
     - IncomingMessage, ImmediateMessage: ofono_incoming_sms_cb_add()
  - Message:
     - Cancel(): ofono_sent_sms_cancel()
     - State: ofono_sent_sms_state_get()

sms_class = 0 means immediate messages (just popup, not going to
application and history), while 1 means regular messages (goes to all
of popup, application and history).