XWIKI-9543: Activity Stream should ignore some events.
XWIKI-9543: Activity Stream should ignore some events.

* HiddenEvent renamed to TransientEvent.
Merge remote-tracking branch 'upstream/master' into XWIKI-9543-2
Merge remote-tracking branch 'upstream/master' into XWIKI-9543-2
XWIKI-9543: Activity Stream should ignore some events.

* Use BeginFoldEvent and EndFoldEvent.
Merge pull request #189 from gdelhumeau/XWIKI-9543-2

XWIKI-9543: Activity Stream should ignore some events.