Background image input should only support image uploads

[neeraj3029]

I'm submitting a ... (check one with "x")

• [x] bug report
• [ ] feature request
• [ ] support request => Please do not submit support requests here, instead ask your query in our Gitter channel

Current behavior:

Currently any type of file can be uploaded in "Background image" upload setion.

Expected behavior: Only image uploads should be allowed.

Steps to reproduce: Try uploading a non-image file.

GIF-

System information:

Your operating system: MacOS

Would you like to work on the issue? Yes