Add expand-node-at-point and contract-node-at-point function to Expand / Contract bracketed list according to node type at point (array, object, function, call args).

Removed previous ea ca eo co eu cu ec cc key bindings.

Breaking change in 0.7.0:

js2-refactor.el is now a minor mode that has to be enabled, with
something like the following:

(add-hook 'js2-mode-hook #'js2-refactor-mode)