Add receivedOn time stamp to GerritTriggeredEvent.

Gerrit events can be processed by more than one thread so there is no
garantee that events listeners will get notified for each event in the
same order they were received. Add receivedOn time stamp so listeners
have a way to know if an event came in before/after another one.

Change-Id: I566b6ee2263729e6df2409ebe1dc62110053b9e1
Add RepositoryModifiedEvent interface

RepositoryModifiedEvent represents any event raised by a ref created/changed in
the git repository (PatchsetCreated, DraftCreated and RefUpdated).

An example of usage is the gerrit-trigger: to implement wait for
replication feature, when a GerritEvent is interesting, it must wait
for replication to be complete before starting the build but only for
events that created/changed a ref in the git repository.

Change-Id: Icaec80452e4753ee80b38084978953578b488514
Merge branch 'more'

Conflicts:
	src/main/java/com/sonymobile/tools/gerrit/gerritevents/dto/events/DraftPublished.java
	src/main/java/com/sonymobile/tools/gerrit/gerritevents/dto/events/PatchsetCreated.java
	src/main/java/com/sonymobile/tools/gerrit/gerritevents/dto/events/RefUpdated.java
	src/main/java/com/sonymobile/tools/gerrit/gerritevents/workers/AbstractJsonObjectWork.java