Some Yesod cleanup/optimization

* Use sendWaiResponse
* Simplify the Mongo code to avoid persistent-mongoDB
* Avoid InternalState acquisition
* Use runInUnboundThread for Yesod
Use stylish-haskell on yesod.hs
Reduce library dependencies in yesod
Update WAI to use GHC 7.8

Pinging @kazu-yamamoto
Pass in explicit core count from threads variable

Pinging @kazu-yamamoto does this make sense to you?
Merge pull request #1086 from snoyberg/master

Updates to Yesod and WAI
LGTM!