Do some checks in liaison form

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

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* Check that entered emails are valid email adresses
* Check that there is no existing liaison with the same title entered on the form

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_Issue migrated from trac:375 at 2022-03-04 01:02:05 +0000_