Creates SpringyCarousel project to demonstrate UIDynamics with CollnView
Creates basic collection view flow layout

Really simple content - just tiles with a number in. At the moment,
although we have a subclass of the flow layout it has no custom behaviour.
Add implementation to create horizontal line collection view

Really simple stuff - enforce horizontal scrolling and push all the content
down the the bottom of the view with a contentInset.
Adds basic UIDynamics behaviour

We connect the cells to springs and then stretch them a distance proportional
to their distance from the touch point. Need to refine some values - and
consider whether we should try a full grid instead.

Also want to work on the gravity drop and bounce for inserting a new
view.
Adds the ability to create new tiles

The new tile gets inserted roughly in the middle of the currently
visible views. This is pretty much all coming from the collection view
api. Need to work at adding UIDynamics to this adding process.

There is currently a problem with the tiles at the right hand side not
displaying correctly once new ones have been inserted.
The animation for new tiles is now managed by UIDynamics

This code is currently quite buggy. It's not particularly clear how to
improve this right now, but at least it's there. I reckon tidying up the
behaviours to make them more coherent will go a long way to fixing the
problems we're seeing here.
INTERIM COMMIT

This commit is a WIP, and is for data transfer only
Updates for the new API and fixes the pushing backwards bug

The crash was because the items weren't being removed from the global
behaviours - i.e. the gravity. Therefore an item would come into view
and need updating using the dynamic animator, but would no longer exist.
We now check to remove items based on their indexPath.
Adds the new item adding code back in

Simplified it a little and now it works nicely :)
Refactor to fix an insertion bug, and to make the code more sensible

We now save attachment behaviours in a dictionary indexed by index path
rather than UICollectionViewLayoutAttributes. This makes some of the logic
slightly more complicated, but greatly simplifies removal of items.
Adds first draft of the writeup, and refactors a layout method

Need to add some pictures and proof read. It might be too long and need
splitting in 2.
Fixed some old code in the writeup and added some images.
Adds the correct license header to the source files
Fix some writeup inconsistencies
Merge branch 'days/05-uidynamics-collectionview'