Plugins BeatIt

Two minor changes

• Added a bit more detail to the output when no AudioSource is found.
• Added two more test objects to the scene that have sound in them (Button, AudioSource).
  

After a prompt by @BlackMagic, I realised that the code for automatically searching the AudioSource of the atom was weird (hey, that was my first plugin ever... so I am excused) and missed the HeadAudio of a person when attached to one. Fixed now. The demo scene has a new button ("V") that makes her say something and the eyes flash based on the spoken words driven by the BeatIt plugin on the "Woman" atom.

I added a few more lines of description of how to use the plugin.

Removed the dependency of Timeline after discussion with @VirtAmateur. Also, learned a bit more about the in-build Animation system that way.