The -dev packages do not include XML files for dbus API definition

In order to use the QtDbus API properly, one must generate some code from the XML files which define the DBUS API. Unfortunately, these files for ubuntu-download-manager are not included in the -dev packages of the appropriate libraries, and so when using the tool to generate the code, one ends up with comments including paths which are useless to other developers, and it's not sensible to include build rules which automate the process. For example:

+ * Command line was: qdbusxml2cpp -v -c DownloadTrackerAdaptor -p downloadtrackeradaptor.h:downloadtrackeradaptor.cpp -i metatypes.h ../../../../../../ubuntu-download-manager/trunk/docs/dbus/com.canonical.applications.download.xml