added a storage service so that we can download images to an appropriate directory and thus manage deletion per event. also created a link from event to speaker since this cleans up the fetch request
Merge branch 'master' of https://github.com/TEDxCT/tedx_ios

Conflicts:
	TEDxCT.xcodeproj/project.pbxproj
	TEDxCT.xcodeproj/project.xcworkspace/xcshareddata/TEDxCT.xccheckout
	TEDxCT/TEDxCT.xcdatamodeld/TEDxCT.xcdatamodel/contents
added a TEDImageDownloader that integrates with the storage service to provide an image downloading framework that provides callback blocks and saves images to disk.
Merge branch 'master' of https://github.com/TEDxCT/tedx_ios

Conflicts:
	TEDxCT.xcodeproj/project.pbxproj
	TEDxCT/Models/CoreData/TEDEvent.h
	TEDxCT/Models/CoreData/TEDEvent.m
	TEDxCT/TEDxCT.xcdatamodeld/TEDxCT.xcdatamodel/contents