rename all data services: FooData -> FooEndpoint

Summary: just a name refactoring

Test Plan:
* app should work exactly like before
* specs (currently only e2e protractor specs) should still be green
  * start the app at localhost:8080, using the real backend
    * gulp --nodeserver
  * run protractor specs; two options here:
    * protractor test/protractor-conf.js
    * (sudo) npm run protractor

Reviewers: rjmackay, seth, shadowhand

Reviewed By: seth, shadowhand

Subscribers: seth

Differential Revision: https://phabricator.ushahidi.com/D406