Contacts: Editing better validate inputs

[bernhardreiter]

Right now (a6c54bf3f266f230cba0dd1a4c0cbdcd22345c73) only some basic validation is done on input fields (e.g. number input for format_id or sector_id). It is possible to add better validations like if an email-address looks like one. Validation will never be perfect anyway, so this needs some idea when it is good enough.