Added folder generation / Layer names

Implementation proposition.
- Refactored code to use UIView instead of CALayer
    -> Allows use to retrieve View class, and useful properties
- Added layer grouping
    -> Group is rootview is a container view
    -> UIScrollView (So UITableView and UICollectionView will also work)
    -> Cells (UICollectionViewCell / UITableViewCell)
    -> Header / Footer / ReusableView
- Added layers naming
    -> First check accessibilityLabel
    -> Next, check for text + attributedText property
           -> UILabel, UITextView, UITextField
           -> May be updated, perhaps, to add directly a Text layer in next versions, no ?
    -> Also check for buttons (title / attributedTitle)
    -> Finally, use UIView class name as placeholder
- Added isImageEmpty method
    -> return NO for now, but it may be useful to write a method that will trim empty layers from PSD, no ?
- Updated sample to add a ScrollView, for text purpose
    -> In my opinion, we should create a more complex example, with tableview, etc...
- Old implementation commented, for futur reference
Regards,