Add support to send SMS via frontlinecloud plugin

Summary: Add a reply action to the controller

Test Plan:
Setup frontlinecloud

Execute a post request /frontlinesms/reply

Reviewers: rjmackay, shadowhand

Reviewed By: shadowhand

Subscribers: srutto, lkamau

Maniphest Tasks: T187

Differential Revision: https://phabricator.ushahidi.com/D87