Use implicitly synthesized properties
Make outlineView:shouldExpandItem: a no-op for expanded items

Fixes #160.
Revert "The 10th tab now get ⌘0 as key equivalent"

This commit made the 11th tab get ⌘1 as key equivalent. Fixes #1078.

This reverts commit 5e6cfe8e1ef990d24100c4859c25948d37c8ee04.