Add support for Lucene SuggestStopFilter

The suggest stop filter is an improved version of the stop filter, which
takes stopwords only into account if the last char of a query is a
whitespace. This allows you to keep stopwords, but to allow suggesting for
"a".

Example: Index document content "a word". You are now able to suggest for
"a" and get back results in the completion suggester, if the suggest stop
filter is used on the query side, but will not get back any results for
"a " as this is identified as a stopword.