Bug 1020876 Route desktop client XHRs though the mozLoop API to share hawk implementation with MozLoopService. r=ttaubert

--HG--
rename : browser/components/loop/content/shared/js/client.js => browser/components/loop/content/js/client.js
rename : browser/components/loop/test/shared/client_test.js => browser/components/loop/test/desktop-local/client_test.js
Bug 1032738 Desktop client fails to authenticate session tokens with the latest loop server - change to using a hex key for hawk. r=jparsons