Escape AbuseFilter description properly (disallow wikitext)

Right now the public description of AbuseFilters can contain
wikitext which will be parsed.

With this change the public description will be escaped
everywhere to prevent the parsing of eg. templates on
Special:AbuseFilter/history.

Change-Id: I777cac5fc195819ed296f791d0b8cc3ed2ae9eea
Merge "Escape AbuseFilter description properly (disallow wikitext)"