Split up event grouping logic and added tests

Change-Id: I925d0c74133b5939f2bed249c462c63f063cf46c
Displat "No summary provided" for edit events that have no associated summary

Change-Id: Iccc2c0b5485bc589f06f94984229ae5c692a0b2c
Merge branch 'master' of ssh://review/mediawiki/extensions/EducationProgram