Refactor file chooser (isolate reusable parts)
Remove disableHighlight property from NSCell subclass

The desired rendering can be achieved without adding code to NSCell
More file chooser refactoring (introduce reusable superclass)
Sign embedded bundles

This is required when signing on OS X 10.9.

Although the option is not documented for the version of codesign included with 10.8, using it does not result in an error.

Closes #1158