WebStyle: no crash in invenio.wsgi initialisation

* Avoids crashing in invenio.wsgi during pre-loading of data
  structures. In this way, even in case of bugs in one of the
  calls, the site can still load.

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
I was just worried that if we while developing or running tests or whatever have any errors in that module, it may be shadowed and we would not know right away unless we dig for a while (specially for new devs who probably do not know about this file).

I agree the site should not go down depending on data (like the bad KB entry), but if importing register_exception is not data dependant and will only fail if some code is broken, it should tell us right away and since we never deploy broken code on production we should be fine? :-)