Persist user modifications of Lexical Tables

Lexical Table user edition is not persisted between sessions and no message alert him.

discuss about the possibility to mark/unmark some matrix rows/cols rather than really suppress or fuse them
find a way and a format to store these markers (suppression and fusion) to recreate the result
thought about the solution of store “data” result in the .*prefs persistance file, eg. for LT =>the R data, for charts =>the file data or the serialized Java object

(from redmine: issue id 2545, created on 2019/04/11 by Sebastien Jacquot)