Using `format` for formatting bang queries caused a KeyError for some
searches, such as !hd (HUDOC). In that example, the URL returned in the
bangs json was `http://...#{%22fulltext%22:[%22{}%22]...`, where
standard formatting would not work due to the misidentification of
"fulltext" as a formatting key.
The logic has been updated to just replace the first occurence of "{}"
in the URL returned by the bangs dict.
Fixes#513
ddf951de35