Bug 947139 - [DSDS][Message] Send message via default SIM r=francisco

This refactors the sendSMS and sendMMS methods in MessageManager, and passes the
serviceId all the way from the UI to the API.

This also styles the composer for DSDS configurations, and display the correct
SIM inside the button.
Merge pull request #17139 from julienw/947139-send-default-sim

Bug 947139 - [DSDS][Message] Send message via default SIM r=schung