Create option to use Dispatch as HttpAdapter

Currently, we have to use spray+akka to for http requests. This causes dependency clashes with Spark which are very hard to deal with, so we decided to take advantage of the ability to pass in an adapter. We're still defaulting to the current adapter, which has been renamed to HttpAdapterSpray, which itself inherits from the HttpAdapter trait.

Changes:
    Break apart HttpAdapter into Spray & Dispatch

    * Create new HttpAdapter trait with methods of current
    * Rename current HttpAdapter to HttpAdapterSpray
    * Create HttpAdapterDispatch
    * Add tests

    Bump version 1.0.1