Created a playground to demonstrate designated initialisers

This is just the default one for now
Completes a simple swift playground which demonstrates initialisation

There are a couple of classes, Person and Ninja. Might need some more
work when the writeup begins
Writing about designated initialisers

Need to finish subclassing and objc
Completes writeup about designated initialisers
Adds the daily thumbnail
Added the link to the index page
Update to match the new array syntax
Update the writeup to match the new array syntax
Merge branch 'days/09-designated-initialisers'