Implement DNA intro animation (still incomplete)

[#47730701]
Add SVG images required by DNA intro animation

[#47730701]
Add playIntro() method to genetic properties class

[#47730701]
Add playDNAIntro() function to MD2D Scripting API

[#47730701]
Update "Modeling Transcription" interactive, let user play DNA intro

[#47730701]