We'll force it in stack-8.0.yaml because its closest to the LTS that
will actually have it. Not even nightly has aeson-1.1 yet, since
they're trying to get as many packages onboard as possible beforehand.
This commit moves bloodhound library to use elastic 5.0.
The filter type was changes to be a wrapper for queries, and some
new APIs are met.
It is *not* feture-complete, however, all tests pass.
