Merge pull request #712 from simong/push-notifications-sockjs

Push notifications
(Release 4.0.0) Bump version
(Release 4.0.0) Remove shrinkwrap
(Unrelease 4.0.0) Roll back tagging
Merge pull request #754 from simong/push-notifications-sockjs

Allow content-comment and discussion-message propagation
(Release 4.0.0) Bump version
(Release 4.0.0) Remove shrinkwrap
Excluding the module test utilities (module/lib/test)
Added unit tests for some low hanging fruit:

 * Config - getLastUpdated
 * Docs - getModuleDocumentation & getModules
 * Removed unused ImageUtil.downScale and added tests for ImageUtil.convertToJPG
Added some unit tests for the content storage backends
Enable preview processing on Travis CI
Propagating tests exit code in Grunt
Removed 'excluding pp tests' in README.md
Add a note about etherpad-lite @ 1.2.91 in the README
Simple test for preview reprocessing
Added a test that verifies previews can be reprocessed with a revision filter