Added methods to hold HUD with completion state until dismissed by tap.

[ryanmsmith]

I needed to have the success or error completion state hold on screen to show an action had been completed to a potentially distracted user. The methods I added allow the HUD to hold until the user taps to dismiss.

[larsacus]

I'm going to keep this pull request open for now. I'm not sure that the use-case is generic enough to pull into the project at this time.