Typewriter effect

[HugoGranstrom]

Two new blocks that add a typewriter effect so it looks like someone is typing them. Example: https://www.w3schools.com/howto/howto_js_typewriter.asp

• [x] typeText: takes text and pace as inputs. Implemented in #5
• [ ] typeCode: needs to take the static highlighting into account or else random HTML tags will pop up out of nowhere.

Problems:

• ~~How to make it start when the slide is visible, or even when a fragment is showing it? By default it will start when the page loads I guess~~ nbCodeToJs to the rescue!
• Reveal rewrites the code blocks so we might have to parse their code to start with.