chore(ui): refactor Steps molecule so it works with Styleguidist
- Make step title optional to support eLife design
- Move docs into component
- Otherwise they are likely to be forgotten in the MD file
- Styleguidist parses the file and builds a table of props
- But it doesn't understand HOCs
- So refactor into plain component
I don't think this changes the behaviour in any meaningful way but I'll admit I found the previous code a bit hard to understand so please point out if I've missed something.