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.
add sprite kit texture atlas script to pbxproj
sk texture atlas gen minro changes
Publisher: SK spritesheet check tool exists, additional warnings/errors
pbxproj: remove texture atlas script, added txt file with location to texture atlas tool
pbxproj: changed the target for the texture atlas tool .txt file
Publisher: cleanup
Merge branch 'develop' of github.com:apportable/SpriteBuilder into develop-steffen

Conflicts:
	SpriteBuilder/SpriteBuilder.xcodeproj/project.pbxproj
Fixed: Drag and dropping different resource types will disable dragging #297. Solution: prohibit dropping multiple types.
Bugfix for issue #46 Deleting folder with Interface files nested underneath, and then saving.
If a tab was open for a certain file and that file was deleted by deleting a parent folder the tab would be kept open. Saving now caused the crash since there was no valid currentDocument any more.
Solution: Close the tab as soon as a file gets deleted by deleted parents.
SB: publisher exports spriteFrame property first (Sprite Kit exports only)
Merge branch 'develop' of github.com:apportable/SpriteBuilder into develop-steffen

Conflicts:
	SpriteBuilder/SpriteBuilder.xcodeproj/project.pbxproj
update SB+SK submodule ref
Ignoring CocoaPod files(future stuff) and AppCode project related files.