Move Flags.css into Repo

[Liam]

I noticed that the demo relies on a flag.css file which appears to be hosted externally on Github

jQuery-QueryBuilder/examples/index.html

Line 17 in 2a1404c

 <link rel="stylesheet" href="http://mistic100.github.io/jQuery-QueryBuilder/assets/flags/flags.css"> 

It might be nice to bring this file and its related image into the repo

[Damien Sorel]

It's in the gh-pages branch https://github.com/mistic100/jQuery-QueryBuilder/tree/gh-pages/assets/flags