NXP-15025 activity background works should'nt list unpredictable results length

Conflicts:
	nuxeo-admin-center/nuxeo-admin-center/src/main/resources/web/nuxeo.war/incl/usersActivity/workmanager.xhtml
NXP-15783: make sure the cache is up to date before indexing

Conflicts:
	nuxeo-elasticsearch/nuxeo-elasticsearch-core/src/main/java/org/nuxeo/elasticsearch/work/ChildrenIndexingWorker.java