Added PlayTimeline command

[GuroGuru]

Description

This PR is a new feature, the command PlayTimeline.

What is the current behavior?

Currently Fungus animation-related commands don't compreehend the Unity Timeline functionality, importing sequencing tool.
Issue Number: #627

What is the new behavior?

The new command PlayTimeline allows specifying a Timeline object from the scene and play it during the flow. It also allows choosing whether if the flow will be blocked until the timeline stops or if it will continue the execution.

Important Notes

• My change adds tests or test scenes
• My change adds demos to FungusExamples

Other information

[breadnone]

Perhaps restructure it better to be inline with Fungus coding standards. Any wait operations usually called waitUntilFinished.

And you can wrap your if condition for continue inside your delegate function to reduce code duplication

Something like this

            if (timeline != null)
            {
               timeline.stopped += delegate 
               {
                  if(waitUntilFinished)
                  Continue();
               };
            }
            if(!waitUntilFinished)
            {
                Continue();
            }```

[GuroGuru]

@breadnone, thanks for the tip! By the weekend I'll update the code based on your suggestion.