Fix can edit row for item selector check

This pull request fixes 3 things.

1. The correct selector is checked for the the `treeView:canEditRowForItem:treeNodeInfo:` dataSource method
2. The value is returned from the `treeView:canEditRowForItem:treeNodeInfo:` dataSource. Otherwise the return is always `YES`.
3. Adds a standard .gitignore file so that Xcode settings are not checked in