Migrate from isomorphic-fetch to fetch-everywhere (React Native support)

[aarondancer]

This pull request replaces isomorphic-fetch with fetch-everywhere to support React Native. React Native support has been requested in these issues: #119 #111 #106

[coveralls]

Coverage decreased (-0.7%) to 99.273% when pulling ec5d169 on makeshopio:master into e72ac27 on agraboso:master.

[mlippens]

I think an import of fetch should be removed. According to the specs, fetch is supposed to be global, and therefore my vote goes out to do it that way as well. Let fetch be global, and let redux-middleware-api use the global. That way anyone can choose for his own environment what polyfill to use.

[agraboso]

The next branch (which will lead to version 2) removes isomorphic-fetch in favor of the global fetch.