Issue #147: Added mediators model.
Added get and getAll API endpoints +Tests.
Stubbed add endpoint.
Issue #147: Added tests for addMediator.
Issue #147: Added functionality for addMediator.
Merge branch 'master' of https://github.com/jembi/openhim-core-js into register-mediators

Conflicts:
	src/koaApi.coffee
PR #203: Only admin users should be able to add mediators.
Merge pull request #203 from jembi/register-mediators

Register mediators