HAFAS XML: Considerable improvement in XML parsing time

Use of `QDomDocument` instead of `QXmlQuery` to parse XML response
brings improvement in parsing speed by the factor of up to 50 times,
depending on the platform and device.

See #121 - Slow parser performance
HAFAS XML: Fix typo
HAFAS XML: Indicate that error comes form the backend

There are some error messages generated by the service that might trick
users to think that the error is reported by the client, not by the
service. For example, OBB can return "An error occured." message.

To avoid this confusion, all error messages that come from the service
are now prepended with "<servicename> replied: ".
No need in Qt XML Patterns module anymore
Fix: QXmlResultItems was included but not used

Unneeded include was removed.
Merge pull request #122 from leppa/parser

HAFAS XML: Considerable improvement in XML parsing time