Allow multiple sections to be closed programmatically

I'm looking to be able to close sections programmatically.

Use case: You have 3 sections, but only one should be open at a time. Let's say section 0 is already open. If you select section 2, section 0 should automatically be closed.

The issue:
``didSelectTitleCell`` uses ``[self.tableView indexPathForSelectedRow];``. When you are programmatically closing a section, the index path will be nil.

Solving the issue:
Added an extra function and variable that lets you specify which section is the one being animated.