Add Tracepoints for issue 1837

* src/gpgoladdin.cpp (GpgolRibbonExtender::GetCustomUI),
 src/ribbon-callbacks.cpp (getIcon): Add Tracepoints.

User kjathome reports seemingly random crashed in issue1837
where at least outlook thinks that they happen in the getIcon
and GetCustomUI callbacks. As this is both pretty static code
I am clueless why they would crash randomly.

This Trace output might give us a better idea. It should be
reverted before a release.