rest/api-doc: Add preliminary section for /mail/ service
rest/api-doc: White spaces fixed for better sections rendering
rest/api-doc: Update '/info/' service to add "contexts" information

Contexts are basically main folders known to the backend
mock/rest: Run mock server on port 5001 not to collide with ocsmanager
mock/rest/test: Add test for /info/ service
mock/rest: Add 'contexts' to result from 'info' service