Implement detail view

[Jakub Šturc]

On detail view you should have a option to download picture in sizes:

• Original size
• max(width, height) = 1920
• max(width, height) = 720
• max(width, height) = 340

Aspect ratio should be always preserved.

Since preferred sizes are likely to change in the future do resizing on the fly.

Please preserve the original format picture extension (.jpg, jpeg, .png, ...)