Settings customization with defaults from the Sublime jsformat

Hey again, one more small one that adds basic jsformat options to the settings panel for the plugin.

Atom has a rather limited mechanism for specifying how settings should be presented so limited fields like brace_style have no validation at the moment.

Fixes #4 (although doesn't add format on save as was suggested in a comment, that should be a separate issue)

Also #5 is now fixed.