[bug 949101] Add mlt section to response view

This adds a morelikethis section to the response view. It's "prototype"
quality. I had a hard time fine-tuning the MLT query and ended up just
adding a massive stopwords list which seemed to reduce the number of
"wow--that has nothing to do with this" responses. This might benefit
from synonyms if we ever add that.

This also adds a test for the response view to make sure the "secret"
section only shows up for analyzers.
Cosmetic: change to imports
Cosmetic: Remove dead code
Fix bigrams computation

This switches computing bigrams to use the standard analyzer rather than
the snowball analyzer because then we don't get stemmed weirdness.
Simplify and speed up indexing

This removes some code from indexing that we don't really need and
allows us to switch to a list comprehension which speeds things up.