Use simple-prefs instead of simple-storage for saving rules

[j-hao]

1. use simple-prefs instead of simple-storage due to ss instability this will hopefully fix issue #13 See detail about ss issue https://bugzilla.mozilla.org/show_bug.cgi?id=1091244
2. move GooRule to data/js otherwise option page will complain not found it See http://stackoverflow.com/questions/22656494/contentscriptfile-dont-work-in-pagemod and https://developer.mozilla.org/en-US/Add-ons/SDK/Guides/Content_Scripts/Loading_Content_Scripts
3. add main field in package.json in order to work with jpm