Bug 848519 - Part 1: Move files. r=gavin

--HG--
rename : services/common/preferences.js => toolkit/modules/Preferences.jsm
rename : services/common/tests/unit/test_preferences.js => toolkit/modules/tests/xpcshell/test_Preferences.js
Bug 848519 - Part 2: Update Makefile.in and test harness. r=gavin
Bug 848519 - Part 3: Replace services-common/preferences.js with gre/modules/Preferences.jsm in imports. r=gavin