Turn backdoor module type into REST

Backdoor module type was defined. As a part of backdoor testkit, backdoor-rest-plugin will turn the backdoor module into REST. At this time, plugin developer can access their backdoor via <baseUrl>/backdoor/[path]/[resource]

The test for this plugin will be done by integration test. Here is the test plan : https://docs.google.com/a/atlassian.com/spreadsheets/d/1QYxqgfaspVbc66ug1ff42K8lEglcaauGsE2M1a1ww3c/edit#gid=0