Use asynchronous sending of sms or mms

Adding more as a placeholder for development consideration of nice to have.

Environment: phosh 0.17.0-1pureos1, chatty i A 0.6.3.

Use Case: Allow user to draft and send message even when modem isnt available, connectivity is poor, or modem is available but there is no network connectivity. On re establishing network connection, connectivity, with powered up modem the que is processed FIFO (first in first out).

Currently: two states exist, message sent and succeeded, or message sent and failed, this is adding a third state of message sent and in que.