rex_sql: added set/getDateTimeValue()
use datetime for createdate/updatedate
use datetime for lasttrydate
use datetime for nexttime/execution_start
use unix timestamps, added constant for sql datetime format
do not use NOW()
do not use DateTime objects
fixed indentation and docs
fixed updatedate timestamp, it's already a unix timestamp
use rex_sql::datetime()
better comments
Merge pull request #271 from redaxo/datetime

Datenbank: echte DATETIME-Felder verwenden