Add database username/password as settings

Installations which require username and password to access external databases have no good way to define this in the deploy configuration. The workaround is to add this information to the "dir" property as the comment to FR 2039 by Nicolas shows.
JOLF comment from FR 2039:
"I was not aware of the user/passwords features of the JDBC URL
since we have not used them in DK.
It is an obviously extension to settings to add the user and
the password:
settings.common.database.user
settings.common.database.password
These features should also be applied to the admin database.
Estimate: 1 md.
"