Add "X" button in toast bar

[Vituli]

When using a toast with an infinite duration, it would be nice to have an 'X' button that allows the user to close the toast themselves.

[jhonatanAlanFerreira]

I am using the toast.promisse() and it is being hard to manually implement it, because in this case it doesn't allow message with html, just plaintext. A 'x' button option would be very nice.

I created the PR #354

[ADTC]

@Vituli @jhonatanAlanFerreira why not just use the ToastBar function-as-a-child example for adding a dismiss button in all toasts, but remove the condition t.type !== 'loading' so it also shows on loading toasts (which have infinite duration)?