tasks #7238 Deal with default pages

This task is part of story #7028 Search in wiki pages

Default pages are not indexed. If we modify them, they are indexed.
If we delete a default phpwiki page in phpwiki service, it's deleted in
ElasticSearch only if it was previously indexed

Change-Id: Id15b6ad877f699d7f928195c84ad10bf7a0617da
Merge commit 'refs/changes/86/2786/1' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7238 Deal with default pages

Change-Id: Ie45674494d3687d690055301604fbbaaaa3d9f26
This is Tuleap 7.2.99.61

Change-Id: I09eca2a74c4740c55dca7923adba191128ba3da3