Fixes for LT-12986 and LT-12989

* Lexical relations not present in the new lift data will be deleted
  when using the MergeStyle.MsKeepOnlyNew
* Export will now include custom relation type in a trait and import
  will use that when it is found to create it.
* Refactored code

Change-Id: I9430f19c454704c9f8f6354d67067fa39eb696df