Tree: Copy ilTree methods to NestedSet and MaterializedPathTree ...

[lukastocker]

... and adjust files with ilTree references to Nested or Materialized Tree accordingly.

[klees]

Hi @fwolf-ilias,

with this change we try to bring a little more order to the relation of ilTree, ilNestedSetTree and ilMaterializedPathTree:

• ilTree will use the other two, but not the other way round. It will basically be "the ILIAS Tree" after this change.
• ilNestedSetTree will not know about ilTree anymore. Many (previous) usage locations of ilTree that can actually only use nested set implementation will do so in the future.
• ilMaterializedPath can work as standalone implementation as well.

Feel free to contact us for discussion or questions, ofc.

Kind regards!