Implement symmetrical index import feature

[DmitryKey]

Luke can export index, but not import the produced xml to create an index. This ticket is to make such a tool.

[mocobeta]

In my personal view, it is not possible to "index import" without original data and analysis chain information.
For example, Elasticsearch "reindex" feature obviously uses their analyzer and mappings information. But Lucene itself does not preserve such meta data of index.

Can you clarify the "import index" feature you consider here?