[BUGFIX] Invalid method signature for t3lib_tree_extdirect_Node::toArray()

Method toArray() from t3lib_tree_Node is not properly overriden in subclasses.

Furthermore, many phpDoc comments are wrongly returning void instead of bool.

Change-Id: I99bea296df305673d5c111fc9e5b92ea42599c5f
Fixes: #30060
Releases: 4.6
Reviewed-on: http://review.typo3.org/5088
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers