background.js:
1. fix: when user choose "disable", do not show the text in the context menu when do the right selection click
2. function rewrite and write more comments

script.js:
in FB, the ads sometimes has different class,
so add a new filter situation
Merge pull request #1 from FarmerKing/master

https://www.facebook.com/groups/1434527033427607/permalink/1441259192754391/