* Rename "useLegacyParentChildMechanism" to "hierarchyMode".
* Stop pretending parent child mechanism is deprecated. Is is just off by default.

* Do not display the "edit parent" functionality if the legacy parent/child mechanism is disabled

* Minor improvement: support main page set in the wiki descriptor instead of "Main.WebHome"

* This commit introduces:
** a "core.useLegacyParentChildMechanism" property to use or not the hierarchy based on legacy parent/child relationship
** a "parentchild" script service to get the legacy parents of a document and to get if the legacy mechanism is used or not
** the support of both modes in flamingo
** use the home icon for the Main space
* This first version does not hide some parts of the breadcrumb if it is too long
* This commits does not fix the failing functional tests

[Misc] Try to debug a flickering issue for the Mail Test. The idea is to check if the problem comes from the Mail Module or not.

- Also added unit test for the conversion from ActivityEvent to WatchListEvent.

Revert "XWIKI-12306: A custom displayer should be executed in the security context of the document where it is located."

This reverts commit 7db1cf1c.

Reason: Doing it in 7.2M2 instead.

This reverts commit 739cf0e0.

This reverts commit eebe3051.

* Treat the value of the space field from the database as local space reference instead of space name.

[Misc] Adjust legend to match the fact that w're counting active installs for a week for the history graph

* Refactor a bit the code so that the refactoring jobs are not aware of nested documents but of nested spaces.
* Add unit tests

XWIKI-12306: A custom displayer should be executed in the security context of the document where it is located.

- Fixed failing test by properly applying the AdminSheet in space administration for an unexistent WebPreferences document.
-- The previous getRenderedContent approach was not setting the right sdoc.

- Minor codestyle improvements and javadoc

- Fixed tests

- Made the script right to DENY by default and to no longer be implied by edit. The rationale is that it will be set to ALLOW in the standard distribution's main wiki XWikiPreferences and the admin can DENY it if needed.

- Replaced deprecated usage in SkinAction

* cleanup

- Properly handled both top level terminal and non-terminal WebHome documents.
- Added unit tests.

* remove progressManager.endStep() calls that were not needed
* copy the WebPreferences (child) document when moving a document with deep=false in order to preserve the access rights at the new location
* use the EntityReferenceTree to ensure we iterate the document hierarchy in the right order (depth first) when deep=true
* Update the back-links and the relative links from the document content when performing a move/rename

* Update test coverage ratio.

* fix space open/close jingling bug

* Apply Thomas' suggestions

* fix unit tests

- Using new IDs for the spaceReference and name fields
- Added is/setTerminalPage methods

- Fixed the edit panels since they were not using the UIx mechanism as they were probably forgotten in the refactoring. They were failing to execute because they were using the deprecated #displayPanel macro.

- Checking script rights on the content author of the document where the title comes from instead of the current security document.

- Also added clirr exclusion.

- Deprecaed both core and api methods
- Replaced their usage in xwiki-plaform with #evaluate

* Add ability to disable the space redirect and fix the Scheduler test