Add some more oom helpers
* src/oomhelp.cpp (get_strong_reference): New obtain a strong reference through the application object. (invoke_oom_method_with_params): New. Useful helper. (invoke_oom_method): Use invoke_oom_method_with_params.
The get_strong_reference code is left over from experiments how
to fix the occassional crash when sending. Didn't work but it
might be useful in the future.