Updated example and added spacings

[ChristRm]

Pull request contains:

1. Update an example project:

• I made a small correct of example cell so there is no white rectangle out of shape
• I enabled a selection in example as the purpose of tags is to be able to select them

2. I added 2 methods to delegate:

func tagCellLayoutInteritemHorizontalSpacing(layout: TagCellLayout) -> CGFloat func tagCellLayoutInteritemVerticalSpacing(layout: TagCellLayout) -> CGFloat

I'm not sure that values these methods provide are used in correct places of layout calculating but it seems to work.