New hook 'LocalisationChecksBlacklist' to allow to extend the localisation checks blacklist

The point is to allow to use the blacklist of translatewiki.net,
so the format of $checkBlacklist got changed to be compatible with it.

Change-Id: I5eb328c4bdbb0b21962b89acbe12f46ebb4d9d70
Merge "New hook 'LocalisationChecksBlacklist' to allow to extend the localisation checks blacklist"