Custom files_container_selector

[cwsaylor]

This adds the ability to specify a custom target for the files_container_selector:

$('.attachinary-input').attachinary({ files_container_selector: "#preview-image" })

[itaibenari]

@cwsaylor this is nice, but it breaks the existing api where by one could specify that in data-attachinary.
Instead of replacing the @options if statement it should come after it with else if.