Feature/#1160 package improvements

This implements the second point in https://github.com/spritebuilder/SpriteBuilder/issues/1160.

__Feature looks like this:__

![bildschirmfoto 2014-12-04 um 18 43 31](https://cloud.githubusercontent.com/assets/5259653/5303084/9e060180-7be6-11e4-9af0-9fbc82f022e9.png)


__Working in a way like global auto scaling, override order is:__
`Per asset auto scaling > Package auto scaling > Global auto scaling`


This branch includes the feature as well as a few refactorings:
* New tests added to reflect per package auto scaling values
* Several tests have been adjusted in the course of refactoring
* Renamed PackagePublishSettings to SBPackageSettings
* ResourceManager's createCachedImageFromAuto method was renamed and split into several smaller methods
* ResourceManager's updatedWatchedPaths renamed to updateWatchedPaths
* Publishing and all its subsequent operations require an array of SBPackageSettings to work properly
* Application wide notifications have been altered to set the sender as object parameter and data put in the userInfo dictionary
* Several key constants have been added to access a notification's userInfo dictionary 
* Removed some debug NSLogs
* Some notification names renamed

A little side note: The inbetween solution of a SBPackageSetiingsManager was discarded due to the complexity of the ResourceManager.