startup: Blacklist Opera < 12

jQuery hasn't supported Opera < 12 for several releases now, and
our own support matrix and development practices also consider
Opera 11 and below being Grade C (there are known problems in
Opera 8 and 10, such as missing features and implementation bugs).

Update the blacklist to reflect Opera < 12 being Grade C.

https://www.mediawiki.org/wiki/Compatibility#Browser_support_matrix

Change-Id: Ia2764a49c5d1fad73bd4eb52748269407231700e
Merge "startup: Blacklist Opera < 12"