Compile fix for ARM

Not sure why this is needed, but without this the tomahawk binary fails
to link.

Error:
`.LTHUNK9' referenced in section
`.text._ZN21AccountFactoryWrapperD1Ev[AccountFactoryWrapper::~AccountFactoryWrapper()]'
of CMakeFiles/tomahawk.dir/tomahawk_automoc.cpp.o: defined in discarded
section
`.text._ZN21AccountFactoryWrapperD2Ev[_ZN21AccountFactoryWrapperD5Ev]'
of CMakeFiles/tomahawk.dir/tomahawk_automoc.cpp.o
collect2: ld returned 1 exit status
make[2]: *** [tomahawk] Error 1

src/AccountFactoryWrapper.h

@@ -42,6 +42,7 @@ public:
     };
 
     explicit AccountFactoryWrapper( Tomahawk::Accounts::AccountFactory* factory, QWidget* parent = 0 );
+    virtual ~AccountFactoryWrapper() {}
 
 public slots:
     void openAccountConfig( Tomahawk::Accounts::Account* );