Commit 7a8a00c7057d56350d4b5509cefd812a67d4b7d7 cleaned up the code to move all
files to a dictionary, which accidentally left an undefined "extensionjs_path"
error. Fix that error.
https://bugzilla.gnome.org/show_bug.cgi?id=661623
Update the sample to be more up to date with respect to Shell practices,
and make it look a bit prettier. Additionally, change the file extract
code so that it's easier to update and add new files later.
https://bugzilla.gnome.org/show_bug.cgi?id=653206