Started working on feature #162, some refactoring and preparations to drag multiple items.
Refactoring of addObject to parent to improve readability. Added SB error domain and specific error codes.
Feature working.
Refactoring: Divide and conquer, extract methods where comments were. Some renaming and removed my shortcut to open a specific project on startup.
Fixed: Moving nodes into themselves was possible if placed directly below under the selected node.
Refactoring: removed unused #imports. More extract method. Assert added for not supported index.
Refactoring acceptDrops outline method: extracted methods serving each case.
Fixed: Drag and dropping different resource types will disable dragging #297. Solution: prohibit dropping multiple types.
Merge branch 'develop' into feature/#162_drag_multiple_nodes_on_node

Conflicts:
	SpriteBuilder/SpriteBuilder.xcodeproj/project.pbxproj
	SpriteBuilder/ccBuilder/AppDelegate.m
	SpriteBuilder/ccBuilder/SequencerHandler.m