option to add content of folders (Meteor.AppCache.config.addPaths)

I needed a possibility to add folders and their content.
The story: I have to serve ~6000 files from the public folder (the app has to be self contained at this moment), to make that work I had to hide the folder from meteor's file watcher, because the node would stall with that many files under permanent watch. I achieved this by adding the prefix .# to the folder in public, e.g. public/.#static/folderWithManyImages [1]. After this meteor is completely unaware of the files, I have to serve them manually [2] and because some of them have to go to the app cache (filesystem API seems to be dead) I needed this patch.

I added the option to Meteor.AppCache.config because I wanted to avoid having a settings file, which has to be referenced manually.

[1] https://github.com/meteor/meteor/issues/437
[2] http://stackoverflow.com/questions/11504883/how-to-prevent-meteor-from-watching-files/25161820#25161820

comments very much appreciated! and thank you very much for your fork!