Adds nzbs.in compatability

Updates README.md and Info.plist to include new nzbs.in.js and allow use on
*.nzbs.in domains. Very slight refactoring of nzbs.in.js (originally nzb.su.js)
to allow it to be used as a general newznab template in the future by
changing the "nzbSite" variable definition.
Removes unnecessary executable bits from content_scripts

+x is unnecessary on content_scripts as they're not executed by the OS directly
Merge pull request #9 from joshenders/master

Adds nzbs.in compatibility