Dialog outside click option

For the purpose of A/B tests on dropdowns, `dialog.js` needs a quick & dirty solution that'll prevent dialogs from hiding on clicks outside the dialog itself.

There is currently a function for this but it doesn't work as necessary for the desired behaviour with the dropdowns, so I've added a new `outsideClick` function that simply prevents `_hideOnClick` from doing its job, specifically on popovers that have their own separate `hideOnClick` option set to false.