Work in progress

[thibaudcolas]

This is a work in progress. I case I ever pick it up further, here is where things are at.

• Class components
• SFCs
• PureComponent?
• Simple conversions of props only
• Check the new variables don't shadow existing vars
• Remove duplicate var declarations
• Extend existing destructuring if there is any
• Do not destructure in SFCs if code uses props directly
• Do not put the destructuring as first line of functions for constructor methods
• Do not destructure in the function params for constructor methods