Refactor/project tidy up and sandboxing

Follow up pull request for fixing AppCode tests.
* Sandboxing activated by default for any debug and release builds:
  * Spritebuilder.entitlements used for code signing
  * Code Signing run script phase added again, was removed in previous pull request. If no signing identity is set, the script won't do anything.
  * You can use the debugger now while sandboxed
  * Tests NOT running sandboxed mode
* Removed several warnings, like multiple build commands for images