jsduck: Add 'mediawiki.startUp.js' to eg-iframe

Authored by Krinkle.


jsduck: Add 'mediawiki.startUp.js' to eg-iframe

Follows-up 2ea420eed86. Without this, the startUp() is never called,
and mw.config remains undefined which caused some of the examples
to no longer work properly.

Also move onerror handler to first <script> (follows-up a64a07d).
Exceptions from other code (eg. startup or mediawiki modules),
were not being caught.

Also include 'error' in the line being logged from onerror.

Change-Id: I3956da40b0bd862acab6d4552932aa609c17d569