Adds HttpFetcher and AbstractHttpFetchingProcessStage

Creates a new package in stages/utils/http
Adds sane default to HttpFetchConfigurationBuilder
Adds a plain uri provider to use for default
Explicitly declares runtime exceptions
Added analytics tracking to readme

This adds a tracking image for Google Analytics to the Hydra readme.
Merge pull request #273 from Nycander/http-fetch-stage-helper

Adds HttpFetcher and AbstractHttpFetchingProcessStage