MainWindow: Introduce libraryView

- Loads the image from default location which is hardcoded as of now using NSColelctionVIewDataSource and NSFileManager.
- Uses FlowLayout for showing the items in the collectionView
- Shows Highlight of selection with blue colour (alternateSelectedControlColor).
- Get the index of selection using delegate following NSCollectionViewDelegate protocol and for debugging and all have displayed the log of it to command line.
- Scrolling function is also there with this, when the user resizes Window,it dynamically resizes the collection view items