improved the loading of content scripts

>Instead of always loading jquery, both its plugins, and back.js (a
fairly large file with a lot of functions) on every page we can instead
just load the 9 line file testPage.js which will send a request to the
background page to inject the necessary content scripts along with the
implementation script.
Non-manga pages can be identified in ~ 40ms without loading any
unnecessary files (from my testing).

This is my suggestion for a new method of loading the content scripts and making it a little bit more efficient.
Any thoughts on it? If everyone agrees then this pull request should be merged into the develop branch.