img2img batch upload method

[light-and-ray]

Description

Allow users to drag and drop images in browser for img2img batch. For me it's useful for batch upscalling

Screenshots/videos:

Checklist:

• [x] I have read contributing wiki page
• [x] I have performed a self-review of my own code
• [x] My code follows the style guidelines
• [x] My code passes tests