Add password support for ctkDICOMDatabase

[nicoleaucoin]

The QSqlDatabase supports setting a user name and password on a database. It would be very useful to have that exposed through the ctkDICOMDatabase class (and invokable via Python) via the openDatabase call: https://github.com/commontk/CTK/blob/master/Libs/DICOM/Core/ctkDICOMDatabase.h#L109

[pieper]

Sounds like a good idea to me. Let's be sure this is optional and the API is backwards compatible.

[jcfr]

@naucoin I added few comments in the reference commit.