Allow disabling the "Close modal" button in onboard modals

[liamaharon]

It sometimes makes sense for the completion of onboarding to be compulsory, where the dev doesn't want to handle a 'onboard failed' scenario. This could be achieved by adding the option to disable to top right "close modal" button from the onboard modals.

[cmeisl]

@liamaharon Do we have an actual use case here from any of our integrations?

[liamaharon]

@cmeisl yes, on some pages space-miners and now mintable require the user to be onboarded before the page loads. if the user fails to onboard, the app falls into an error state