Allow to link a liaison with another one

`owner:esanchez@yaco.es` `resolution_fixed` `type_enhancement`   |    by esanchez@yaco.es

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The user inputing a new liaison should be able to select an old liaison statement to link the new one with it. 

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_Issue migrated from trac:381 at 2022-03-04 01:02:37 +0000_