Manually include moc_database.cpp

It consistently makes the build take a couple seconds(!) less than
leaving the compilation of these files to CMake; i have no idea why.

src/database.cpp

@@ -25,3 +25,5 @@ QFuture<void> Database::open(const QString &user, const QString &password)
         }
     });
 }
+
+#include "moc_database.cpp"