Filename can't contain spaces when uploading [BUG]

[cjchirag7]

Describe the bug
When uploading a slide with filename containing spaces, the preview is not available, due to which 'check' fails and user is not able to post the slide.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Upload' button on 'Slides' page
2. Upload any file and enter the new filename with spaces eg. 'my new file.svs'
3. Click on 'Finish Upload'
4. Click on 'Check'

Expected behavior
Either user must be able to create filename with spaces, or the spaces should automatically be converted to '_' to avoid any bug

Screencast
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Ubuntu 18.04
• Browser Chrome
• Version 80.0.3987.132 (Official Build) (64-bit)

[birm]

Thanks for the fix via #344