Switch from n-grams to edge n-grams for suggestions (see #264)

This commit completely switches from n-grams to edge n-grams, so
only suggestions where a token *starts* with the query are returned
(so both `Thomas Mann` and `Mann, Thomas` yield a result, but no
n-grams within a token, e.g. `mas` in this case). This is true for
all queries, but as the n-grams were meant for suggestions in the
first place, I think this might work as the general behavior.

In an attempt to keep things simple, this commit also removes the
manual sorting of results after they are returned from
Elasticsearch. This requirement was caused by the overwhelmingly
large suggestions list (which this commit solves). It also doesn't
make much sense conceptually, since it only sorts the paged result
returned from Elasticsearch, not the entire result set.