Add a close all button for key-value view

[officert]

Add a collapse all button that is enabled when you're in key-value view. Clicking it should collapse any open key-values.

Button could go here somewhere:

[travispett]

Submitted a pull request for this. Not sure if you would want another button to expand all (or to change collapse all to expand all only when collapsed). I am not sure how much of a performance impact there would be with larger collections.