Improved random bg image and added random bg image options

[w00000dy]

This automatically hides the BG image URL field when Random BG image is checked.
If you check Random BG image, Random BG image settings opens up. There, you can decide if you only want grayscaled images, blurred images or both.
If Random BG image is not checked, it looks like this:

If it's checked, it looks like this:

Example with only Grayscale checked:

Example with only Blur checked:

Example with Grayscale and Blur checked: