Updated mediawiki/extensions
Project: mediawiki/extensions/CentralNotice  5a87789bad1e279a4d70d24777f5676b538bf265
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Making CN Pre-Content Handler Aware

There's not much in CentralNotice that actually depends on Content
Handler (introduced 1.21) so I went in and re-added the legacy stuff.
Therefore master should work on 1.20 and probably 1.19.

Change-Id: I9db7c7b83611f1913a4a9eb3bdc3b26417a38cf4