CODING.md: update docs for situation 'new record already saved'.
FillStoreForm.php: In case of form load with r=0, the submitted form element names are does not contain the effective record id - workaround implemented.
Session.php: refactored clear(), create unsetItem().
Sip.php: new buildParamStringFromArray(), updateSipToSession().
Store.php: For r=0 SIPs always add a uniqe parameter.
AbstractBuildForm.php: modified message for subrecords on new record.
QuickFormQuery.php: create unique SIP on form load.