delayed redraw of canvas to display non cached background images

# Conflicts:
#	extension/qfq/qfq/database/Database.php
#	extension/qfq/tests/phpunit/AbstractDatabaseTest.php

Bug #4731 / Dynamic Update: load(post) triggers 'check required' - makes no sense during filling a form - fixed

Bug #4730 / InvalidDate-00-00-2000 FE.type=date - detection of empty date was broken for '00.00.0000'.

Implemented setting 'db_?_xxx' in config.qfq.ini and QuickFormQuery.php and other files. Open: saving in  DB_INDEX_QFQ.

AbstractBuildForm.php: new function subrecordHead(). Replaced several hard coded subrecord column names against constants.

# Conflicts:
#	javascript/src/QfqForm.js