Fixed a few bugs in toasts.

[sirdoombox]

Additions

• Added a button in the toasts page of the demo app to dismiss all active toasts for testing purposes.

Fixes

• Rare case of causing a toast to be dismissed twice by clicking during the animation fixed.
  • API slightly expanded for ISukiToastManager to allow for checking if a toast has or hasn't been dismissed.
• Fix potential source of memory leaks and an issue whereby toasts that were recycled via the toast pool could have their delay-based dismiss action called early or multiple times.
  • This involved expanding the API for ISukiToast to include a property which tracks the currently active delay action, and checking that it's the most recent one so that older delays aren't used early.
• Removed an errant Console.WriteLine that I had stupidly left in whilst I was testing something.

This addresses the issue laid out in #272 along with a few others I discovered along the way.