[finishes #70960174]: add wait command

Now that we have a reasonable model for synchronous execution, I am able to add the oft-requested "wait" block.

The wait block lets you choose between "wait for click", a "random" amount of time, or specific amounts: 1/2 sec, 1 sec, 2 secs, or 5 secs.

The click occurs when the play space is clicked (or tapped).